Sailnet
Tayana List
The following
are messages from the Sailnet Tayana-list covering over 6 years of discussion
about engines, engine problems, suitability when installed in heavy boats, and
engine/prop combinations. The
predominant engine is the Perkins 4-108 with limited discussions about Yanmars.
The problem with engine RPM/boat speed/prop
pitch comparisons is that it is mostly anecdotal
information. The following factors must
be considered:
A)
Adding a larger alternator
changes the pulley size to one with a lesser diameter. RPM’s will indicate 300 to 600 RPM too
high. Most Perkins tachometers are not
adjustable for these changes. Therefore
a boat with the original Perkins tach and a larger alternator will not have
accurate RPM readout.
B)
Different brand propellers with the same pitch
can give dramatically different performances.
Prop brand and model is important.
The original Tayana propellers do not compare well to an identically
sized
C)
Boat speed instruments may
have a slightly fouled impeller or not be calibrated accurately. Currents can confuse GPS Speed-over-ground
readings unless two-way runs are done.
D)
Finally, any speed
comparison is only a snapshot of the boat’s bottom fouling conditions on any
particular day. Only within the first
week after a bottom painting can this factor be discounted.
Here, and also in the archive article “Engines (props-performance).doc”, are
lots of information on prop pitch versus boat speed. Most of it is confusing when trying to make
comparisons among boats of the same type.
In order to enhance comparisons, Tayana owners are asked to provide
updated or new data by filling in the chart below and then sending it to wstrausbaugh@cox.net.
Boat:
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Engine |
Transmission & drive
ratio |
Propeller Pitch &
Brand |
Instruments calibrated? Y/N Tach &
Speed |
Bottom Fouling Clean or ? |
RPM |
Speed |
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Now, the E-mails:
I was wondering what other owners have found to be the optimal propeller pitch?
I am replacing the propeller on my
1978 T37. It has the Perkins 4-108. The previous owner had the pitch changed
and unfortunately the metal must have been bent/heated
too much because it has some deep pits in it, up next to the hub. Not a
galvanic loss like you would see at the edge of the blades. It looks just like it
was bent back and forth , back and forth, until it
fatigued. My pitch is currently 8 and seems to be ok when running the boat
under power. I don't know what it was before because the stamp on the prop is x'ed out and the new 8 is stamped in.
1950 rpm moved the boat 5.5 to 6
knots, and the max rpm was 2950 (8 knots) according to the GPS. Does that sound
about right? By the way, my tach reads 2550 at 1950 rpm and 4000 rpm at 2950!
Looks I have some work to do on the tach. Also I don't completely trust the
speed because the knot meter was probably reading low and the GPS was probably
getting some help from the falling tide. But I'm guessing that the numbers
above are in the ballpark for acceptable readings. Correct? Thanks.
Ray Slaninka 1978 Tayana 37
April 1999
__________________________________________________________________________________
Greg
Just to add to the confusion. Que Tal is a T-37 with a 4108 and a Borg Warner transmission
with a 1.91 reduction ratio. Prop is 18" by 9 pitch. It pushes Que Tal at about 6 knots at 3500 rpm. Red line is 4100. The
formula used by the two prop shops I contacted when shopping for a replacement
(the old prop was cracked) suggested a 16 x 10. When I told them the old one
was 18 x 9 they thought that was in the ballpark and that I should stick with
it if I liked it. The engine shop recommended against over propping in order to
keep the RPM’s down because you don't get the full horsepower out of the engine
if you do. Que Tal does rev
up to the red line, but I only get a couple of additional tenths of a knot. In
fact, I think the engine is most efficient at between 2500 and 3000.
Kent Lewis Tayana 37 April 1999
(According to the Perkins
4-108 manual, the engine has a maximum RPM in displacement pleasure boat
installations of 3600 RPM. Max cruise is
listed as 3000 RPM –
__________________________________________________________________________________
Since I started this thread I've been reading
it with great interest. I have to admit that I am a little confused, but I
guess the old saying "What ever floats (propels) your boat" may apply
here. I've tallied up the responses so far and added a few from marine surveys
of other Tayana's:
- Yanmar 3qm30 and came with an 18 rh 13 prop on a 1
1/4 inch:
- With a Volvo MD3B 36HP, I motor easily 6 to 6.5 knots, 1600 to 1800 RPM, with
a 3 blade Bronze marked Alco 510V 16 X 12:
- T37 with a 4-108. According to my survey the shaft is 1 1/4" and the Prop is 17RH11,
3 blade. (Switched to Autoprop):
- Que Tal is a T-37 with a
4108 and a Borg Warner transmission with a 1.91 reduction ratio. Prop is
18" by 9 pitch.
It pushes Que Tal at
about 6 knots at 3500 rpm. Red line is 4100.
- Sparhawk had a 18 x 12 x1
1/4 RH with Yanmar 3QM30
- From Survey of T-37 thanks to Jim Guin in
- Nautical Weaver has a Perkins 4-108, Borg Warner 1.9:1, and a 18 x 8 x 1 1/4 RH (re pitched from 18 x 10?) Why I'm not
sure other than he said it was sluggish.
I have two more questions just to
make sure I understand over propping. It
means a bigger prop and/or more pitch. Right? And more pitch
means you will move the boat further at the same RPM, which translates to more
speed at a lower RPM. Right? Which means you may not reach max RPM before
you hit hull speed. Right?
Bottom line is I'm not really any
closer to deciding on what prop I should get. Except I know I don't what an
Autoprop (no offense). Maybe I'll take the advice of Patrick Boulter of Barnacle Boulter's in
Little River SC and stop by there on the way up the coast to let him put the
boat and prop to the test. Thanks for everyone's input.
Ray Slaninka S/V The
Lorna Doone April 1999
__________________________________________________________________________________
Interesting discussions but I think that transmission drive ratio's are
needed as well as engine brands to make comparisons. I have a V-42 with a Perkins 4-108 and a
The original factory prop was 18X10 and gave a max speed of 6.3 to 6.5 Kts. Cruise speed was 5.8 at around 2000 RPM. I repitched it 3 times from 18X10 to 17
1/2X11 (no change in performance), 17X12 (picked up a few tenths of a knot and
lost a bit of "thrust" at low speed), & finally 16X13. The smaller
diameter prop is a "speed" prop. That is, it is optimized for speed
in calm water. Speed went to 5.8 Kts at
1800 RPM with about 6.3 Kts at 2000. Top speed was 7.6 but the engine would
immediately start to increase engine water temp. Seven knots was sustainable at 2300 RPM.
Low-end thrust suffered greatly with the small prop. Acceleration was cut in
half and the boat had a hard time maintaining speed with any wave action on the
bow. Moderate pitching (3 to 5 feet)
resulted in 4 knots or less. But the boat cruised well in the ICW. The bottom
line here is that a smaller prop with more pitch equals better speed but less
thrust. I tried another brand of 3-blade prop (maybe a
Then I got an Autoprop. The Autoprop
was easy to install on a V-42. It is an 18 1/4-inch prop. I simply dove under
the boat, placed it on the shaft and tightened the nut. Speeds are now 6.3 at
1800 and 6.6 at 2000 RPM. The engine only has to produce 75 to 80% of its
previous horsepower to achieve RPM and fuel savings are at least 20%. The
engine never labors. Max RPM is 3600 when stopped and 2800 at 7 knots. Top
speed is 7.8 knots but it still runs warm when exceeding hull speed. Thrust is
better than any previous prop I tried as well as acceleration. The boat has
stopped in 50 feet from 5 1/2 knots! Head seas are no longer a problem. Any loss of speed from pitching immediately results in the prop repitching and speed being recovered quickly. Lots
of thrust is available when needed. But the biggest test was when I took
another V-42 in tow and made 5.8 knots at 2300 RPM with only a 5-degree rise in
engine temp (on a 95-degree day in warm water!). The Autoprop is both a
"speed" prop and a "power" or "high thrust" prop.
It is reportedly considerably faster than a MaxProp. It is also expensive. But if an owner thinks that his boat requires
a larger engine and would also appreciate a 20% increase in fuel range, this
type of prop could prove to be a reasonable and money-saving alternative.
__________________________________________________________________________________
NIKIA is
out of the water and we are trying to decide if it is our propeller that is
making us go so slow. At 1800 RPM’s our Perkins 4-108 pushes our Tayana 37 at 5
- 5.5 knots at flat calm. We have a 3 blade fixed prop, 16x19 left handed, I
believe (does this make sense?). I am curious how fast should a boat such as
ours go at 1800 RPM’s? We found out that her fuel consumption shoots up over
1800 RPM’s this is why we stay at that level (where we burn .72 gallon/hr).
What is your experiences?
Alexandra on NIKIA August 1999
__________________________________________________________________________________
Alexandra,
Most of this
is from memory as my documentation is down at the boat, but is close.
The 4-108 redlines at about 4100 RPM
and gets to its max horsepower of 50 at about 3600. At 1800 RPM you are getting
greatly reduced horsepower. According to
the prop shop where I bought my last prop, it is common for people to size
their props for a reduced RPM’s because they don't like to listen to the motor
screaming, but in doing so they lose a lot of power.
Based on my experience, your prop
pitch figure is very high, but maybe it is designed to allow lower RPM’s. On my
4108, the prop calculations indicated a 16x10 prop would allow max RPM’s and
therefore max power. The old prop, which needed to be replaced as it was
cracked, was 18x9 and worked fine. The
prop shop recommended we stay with the 18x9 since it was roughly equivalent to
what the calculations indicated and the calculations are only to get you in the
ball park and then you have to experiment to find the best prop specs for any
given boat. (a heck of a good argument for variable
pitch props) Any way, a pitch of 19 seems huge.
FYI, my prop is right handed, but
that is determined by the transmission and should not be a factor. I burn about
a gallon an hour on my T-37 running at 2700 RPM, which gives me 6.5 - 7 knots,
depending on sea state. The motor just sounds and feels right at that speed.
However, on a miles per gallon basis you are doing a
little better than I am, but I'm getting there faster.
I suggest you call your local prop
shop and give them your engine RPM’s, HP, transmission ratio, and shaft size.
Most of them will be happy to do the calculations over the phone. There is also
a web site that has a prop calculator in it that you can do yourself, but I
lost the address. A good search engine will find it for you. Hope this was helpful.
Kent Lewis SV Que
Tal T-37
#165 August 1999
__________________________________________________________________________________
I have a feathering, 3-blade prop on my T37 with a Perkins 4-108. Since I just purchased the boat, I have no comment except the boat is a dog under power. Max 5.5 to 6 knots under power. The reasoning I received is that the feathering props are less efficient under power due to the lack of "cupping" on the individual blades. But the boat goes like h---- under sail. I do not know what brand it is but I can look it up this weekend and let you know.
Andy T Windy Blue September 1999
__________________________________________________________________________________
Just an incidental comment
..... If your engine is not spinning near the top rpm due to a too large
of pitch or diameter, the engine will not be able to develop sufficient
horsepower; hence, poor performance and low boat speed. Check with the engine
manual for "max" rpm and compare that with your actual "under
load" rpm. (A diesel that is not operating near max rpm at full load is
subject to extreme cylinder pressure causing premature wear, blown head
gaskets, etc.) If there is a great difference, consider a less pitched prop or
have it re-worked. :-)
Rich Hampel - still a Tayana (MKII) Wannabe. September 1999
__________________________________________________________________________________
We have a standard 3 blade (?18x12??), and find it difficult to drive her any higher than 6 to 6.5 under power with our Perkins 4-108.. Under sail, she will quickly accelerate up to 7- 7.5 with our new sails and any sort of a decent breeze.
Harvey Karten September 1999
__________________________________________________________________________________
Concerning
the advice that a diesel should turn near max RPM, I would like to add some
reservations to that.
1) RPM range is dictated primarily by the
transmission drive ratio. Some boats have 2:1 ratios like the
2) A boat with a 2:1 transmission ratio should
never achieve max RPM or anywhere near it. As an example, I have a V-42 with a
Perkins 4-108, a
3) The Autoprop is computer designed for
each boat based on horsepower, transmission drive ratio, hull design, and
displacement. Mine does everything it is supposed to do and appears properly
sized. It will only turn 2600 RPM at my max speed of 7.8 knots at full power.
When the boat is stopped, it will turn 3600 RPM since it uses a much lower
pitch when it senses horsepower applied but no water flowing over the
prop. These RPM’s reflect pretty close
to optimum conditions for this engine/transmission combination and should apply
to a T-37 as well.
__________________________________________________________________________________
I must respectively disagree. An engine produces its maximum horsepower at
a given RPM (and its max torque at a given, though usually different,
RPM). If the engine can't reach that RPM
then you will not get maximum power. In
order to allow an engine to reach its max RPM, and thus assure it being able to
reach its max power, the transmission ratios and the prop must be properly
balanced with respect to each other and the engine.
Given that all three (engine,
transmission and prop) are important, and given that of the three, the prop is
by far the easiest and cheapest to replace, it is usually the one that gets
swapped around to try to achieve max RPM.
The mere fact that a boat will reach
its theoretical hull speed at a low RPM in most situations does not mean that
the prop is properly sized and pitched. In fact, it probably means that it is
either too large or too radically pitched which would result in it bogging the
engine down at higher RPM’s. The real test is will the engine be able to
develop its full HP in severe conditions when it is being asked to punch
through big waves and/or high winds.
I have also had mechanics tell me that
routinely lugging an engine is harmful. Lugging occurs when it is maxed out
under the load it is being ask to carry such that it
cannot rev higher. Allowing it to reach its max RPM will assure that it can get
to the peak of the power curve.
For those reasons, put me down in the max RPM camp.
__________________________________________________________________________________
Is the max power output at a defined RPM also the most efficient level of operation of the Perkins or Yanmar engines? The other issue that I would find helpful in following this discussion would be and efficiency curve of power utilization to speed through the water with different props, but somehow corrected for transmission. (And with a relatively constant loading of displacement). What is RPM for the max power output of the Perkins 4-108? Is it advisable to run it at that level for all day runs? I would assume that with higher speeds (?closer to "hull speed"?), the energy input required increase non-linearly, due to frictional forces, hull resistance, prop inefficiency at higher RPM’s, etc.
The point about not lugging an engine
is something that I have also been taught since I was a boy. But what is that
point in RPM relative to load. Is it a measure of how much the engine RPM is
retarded in percentage when a given load is imposed on it? How does that relate
to the optimal idling speed? On the Perkins, I find that it sets to a smooth
idle at about 900 RPM. When in gear, I find that about 1,000 RPM is the point
at which the engine doesn't increase vibration but allows me to motor slowly in
the anchorage. But what factors should I be attending to?
regards,
__________________________________________________________________________________
You darned
scientists make everything so complicated.
I've never actually seen the power
curve for a 4108, but the good people an Admiralty Marine told me it peaked at
about 3500 RPM. I have no idea if that is the most efficient engine speed in
terms of miles per gallon, but I suspect that that a lot of other variables
enter in to it. As you mentioned earlier, things like load, how smooth the
bottom is, and sea state will effect it. I suspect
each of us is going to have to find out by trial and error on own boats. Given
all those variables, I'm not sure how valuable a generalized efficiency curve
would be, even if one exists.
As for running it all day at the top
of the power curve (not max RPM) , that should be no
problem, assuming a basically sound engine and drive train. Diesels like to work. The problem is can the
crew stand the noise. Sailors want to hear the wind in the rigging, not an
engine and these 37s are not exactly sound proofed.
I assume your assumption about the
non-linearairity (is that a word?) of energy output
is correct.
My seat of the pants approach is to
find a speed where both the engine and I feel comfortable. This summer, plowing
dead into the wind and waves, the engine and I settled on about 2500 RPM.
Coming back two weeks later in a dead calm 2800 seemed about right. In that
case fuel efficiency was greater coming back, but we also had the current with
us so I don't put too much stock in that fact.
A poor answer to your question. Maybe
someone else can do better.
Kent Lewis S/V Que
Tal T-37
#165 October 1999
__________________________________________________________________________________
Agree
completely with Wayne (? – I think he
means
An engine that is lugging will
develop over-pressure conditions within the combustion chamber. The minimal
damage will be a eventual --- blown head gaskets, spun crankshaft bearings,
damaged piston wrist pins .....
Thou shalt
not have an engine with excessive combustion chamber pressure ... for very
long!
Rx: spin the engine between 80% and
90% of max rated rpm. This has been the engineering "rule-of-thumb"
for almost all reciprocating engines for almost 100 years. :-)
Rich Hampel October 1999
__________________________________________________________________________________
Rich,
I'm not sure we disagree and I'm
sorry if my answer was not clear. I did not mean to suggest that you should
routinely run at max RPM. The point I was trying to make is that you should be
able to run at max power.
If by "spin the engine between
80% and 90% of max rated rpm" you mean that is about as fast as you want
to run it for any extended length of time, I would agree. But that is
contingent on not lugging it at that speed. By using a prop that will permit
the engine to reach it's max RPM, you allow it to
easily reach the magic 80 - 90% without lugging. Sizing the prop so it can only
get to the lower RPM, even at full throttle, is by definition lugging it with
all the bad consequences you describe.
According to the local Perkins repair
shop, the max RPM for the 4-108 is 4100. 80-90% of that is 3280 - 3690. Since
the peak of the power curve is about 3500, sizing the prop to allow the engine
to reach max RPM means you can easily and safely run at it's
highest power output without lugging it.
__________________________________________________________________________________
Just to
through my 2 pennies in I have a Yanmar 38hp motor with a 3 to 1 tranny. Engine
max RPM is 3400 cruising RPM is 2800 max RPM is 3150 with the prop I have. The
prop is 4 blade not a type error 4 blade 22 X 14 cut
down to a 17 X 14. My keel is 6 inches wide. Cruising speed at 2800 is 7.2 at
full throttle 3150 I get 8.1. With for blades the ride is very smooth nothing
rattles in the boat.. With such a wide keel and the
boat weighing 28,000 drag was not a factor.
Willi Robles S/V
August Wind October 1999
__________________________________________________________________________________
Well, we have an interesting
discussion going here on engine RPM's and props. But let’s look at some
technical data on the Perkins 4-108 rather than have to rely on the local
mechanic. From a performance chart for the 4-108:
Max torque 78 lbf. ft. (lbf. ft is how Perkins labels it - foot pounds?) at 2300
RPM.
Torque at other RPM's:
1600 – 71
1800 – 75
2000 – 76
2200 - 77.5
2600 – 77
3000 – 74
3600 – 69
. Notice
that the 1800 to 2200 RPM range used by most boats with a 2:1 transmission
ratio is within 3 lbf. ft.
of maximum torque.
Max RPM in displacement pleasure boat installation: 3600 RPM.
Max cruise RPM: 3000 RPM.
Net shaft horsepower is 47 at 4000 RPM and 45 1/2 at 3600.
The Perkins performance chart and the
Perkins advertisement sheet that it came from are now posted on the FTP site as
well as in the Tayana-list Archives, Engines
(props-performance).doc.
Back to the discussion.
I still disagree that "a boat does not have the optimum prop setup if it
cannot reach max RPM at full power". I have never seen an engine with a
fixed 3-bladed prop that would even come close to 3600 RPM with a 2:1
transmission ratio. Not that I have seen that many, but I really have asked
this specific question of owners of boats of various kinds. Note the response from Willi
Robles. He gets 3150 RPM out of the 3400
max RPM allowed on his engine with a 3:1 transmission. This is pretty much what I would expect from
that transmission ratio. I do believe
that if a V-42 or T-37 can cruise between 1800 and 2100 RPM and get 6.5 Kts
that this is pretty much "as good as gets". This
would mean 7 to 7 1/2 KTs at full power (2600 to 2800
RPM's) although I would expect increased engine temps when trying to sustain
over 7 Kts. Sure it would be nice to have a prop that would allow the engine to
rev throughout the complete power range of the engine. But unless you have an
Autoprop, I don't think that this is realistically achievable. The compromise
is the prop/ engine/ transmission setup selected by the engineers at Tayana. For
those who want to run in the higher RPM range, a 3:1 transmission and matching
prop should fill the bill. But let’s
collect some more data... If anyone with a 2:1 transmission ratio can achieve
anywhere close to 3600 RPM with their engine, please give us the details and
your opinion of whether your boat is optimized as far as the prop goes.
The following three messages were the
only ones received in prior years that directly concerned this subject:
Sirena Originally had a 18x12 prop and I was unable to get much above 2200RPM but was able to go 7.5 knots. Yanmar said, "You sail-boaters are always afraid to burn fuel, that engine should be run at 24-2600 rpm with a max RPM of 2800. You will carbon it up and never reach its proper torque HP range. Your prop has to have some pitch taken out...."
So....I had the prop re-pitched to
18x11.25, can now do 24-2600rpm, but can't get above 6 knots.....So there you
have it from me.....Anyone have a 18x12 prop for sale...............
Charles N. T-37
May 2003
Last year we had some discussion on engines overheating and prop pitch.
I had the pitch on mine changed (wish I could remember what it was before) to
16 x 10 (3-blade). It immediately increased my cruising RPM’s from about 1800
to about 2500 without overheating. Boat speed increased slightly. – I get
between 6 and 7 knots at 2500 RPM depending on conditions.
I would definitely recommend
re-pitching as it gets the engine running closer to optimum where you get more
of the horsepower out of it. (though I'm still a long
way from the 3500 to 4000 RPM’s for peak horsepower of a Perkins 4-108)
Mark S/V Windbird Tayana
V-42 cc September 2003
We have a V-42 also but with
the 55HP turbo Yanmar, 2.62 gear ratio and 18' three
blade max prop. The first year I had the Max prop I had to estimate the pitch
(can only really adjust the pitch when the boat is out of water) and the engine
at 2,500 or so pushed her to about 6.8 Kts. However when fully opened, I could
only get 3300 rpm whereas before with the fixed 3 blade we could see red line
of 3500-3600 rpm.
Next year changed Max Prop
to next pitch adjust lower (less pitch) and could get 3550 rpm but at 2500 or
so the boat is only 6.4knts and the engine feels like it has very little load.
To get the same boat speed I need to run 2700+.
__________________________________________________________________________________
I
have spent 5 or 6 summers in
__________________________________________________________________________________
Having the correct pitch allows the engine
cylinder pressure to be a minimum relative value for the horsepower
developed. For instance (as extreme
examples), if too low a pitch: lower rpm developed; hence lower horsepower .... and extremely high cylinder pressure
('lugging' ) , blown head gaskets, bent piston connecting rods, hammered mainshaft bearings, excessive engine wear, etc. If too high
a pitch: cavitating/eroding prop ,
scored cylinder walls, 'hammered' injectors and valve seats, excessive engine
wear.
Most 'steady state' reciprocating engines
'like' to be run (long term) at near 75% of max developed horsepower and at the 75% peak of
their 'power curve'. I like to select
pitch so that I get 75% optimum rpm/horsepower output at the rated hull speed
of the boat. Ever since Drs. Otto and Diesel invented their engines, the value
for long life vs. maximum output has been around 75% rpm/horsepower output. Look at the power curve 'optimum' value in
your engine manual, match/record/correct that value near the hull speed of the
boat and you optimize the whole system for economy, reliability, long life, and
extra power 'bursts' when you need it. For me its like religion, politics,
taking risks, etc.;... I like to be in the 'middle'.
The Autoprop tends to automatically adjust
for the 'optimum' all along the engine power curve. (I just think they are
outrageously expensive, as I can almost do a whole engine rebuild for the price
of an Autoprop.)
Rich Hampel March 2000
__________________________________________________________________________________
The factory told me that if the pitch did
not allow close to full rpm, it was overloading the engine which could have
negative implications over time. Did I read your comment right? Is there a
difference in these two approaches?
David / Hegira March 2000
__________________________________________________________________________________
Yes, you have it right......... ! If you
were underpitched, you would never reach full rpm.
Rich Hampel T-37 March 2000
__________________________________________________________________________________
A friend of mine with a 1996 V-42 has been
concerned about speed under power. Only a little over 6 knots
at full power. He had the prop
cupped last week and now can make 7 knots but is concerned that he can only
turn 3200 RPM. He used to get 3600. The
engine is a Yanmar 4J82E (non-turbo) with a KBW 20 transmission (2.17 drive
ratio). Anybody with a V-42 have that
engine/transmission setup? What kinds of speed-versus-RPM do you get? Anybody
have an Autoprop with that Yanmar? Would appreciate any
comments that I can pass on.
Wayne V-42 (but with a Perkins)
May 2000
__________________________________________________________________________________
Had the hull cleaned the morning we left
Long Island Sound ahead of the Storm on the way back upstate.
The diver did a great job as indicated by the clean hull and prop when we took
her out of the water last Tuesday. I took the heat exchanger off as well as
those items already mentioned and found it surprisingly nice and clean, though
I did pass a brass gun cleaning brush through all the tubes. I will be checking
the impellers this weekend just to see if a fin broke off or something. I even
had the prop re-pitched from the normal 18 x 12.5 to 18 x about 11. I was able to get max rpm under load after
having that done, but still had some high temp alarms at 2400rpm. I thought it might also be my water heater.
The 3Qm doesn't have a thermostat bypass so the heater was connected from the
drain valve of the heat exchanger through the water heater and then tee between
the output side of the engine and input of the thermostat. I also put in a
bleeder valve in the heater line at the
Charles N. T-37 May 2000
__________________________________________________________________________________
We have a V42 also but with the 55HP turbo
Yanmar, 2.62 gear ratio and 18' three blade max prop. The first year I had the Max prop I had to
estimate the pitch (can only really adjust the pitch when the boat is out of
water) and the engine at 2,500 or so pushed her to about 6.8 Kts. However when
fully opened, I could only get 3300 rpm whereas before with the fixed 3 blade
we could see red line of 3500-3600 rpm.
Next year changed Max Prop to next
pitch adjust lower (less pitch) and could get 3550 rpm but at 2500 or so the
boat is only 6.4knts and the engine feels like it has very little load. To get
the same boat speed I need to run 2700+.
We are about to go on a long cruise
of 3000 miles or more and I was thinking about changing back to the original
pitch to get more speed at an efficient rpm that the engine feels comfortable
at and uses less fuel. The guys at PYI (MaxProp) think this is good idea. Do
you or any other readers of this list have experience or thoughts on this
subject?
While
I'm on the prop and related subject, anyone have opinion about SPURS or another
type of line cutter for the V42? Are they useful on the V42 as our shaft comes
out of the keel and has no prop skeg or exposed shaft to speak of for lines to
encircle?
David Laber S/V Hegira
V42
April 2001
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Subject: RPM accuracy
There may be yet another thing worth
checking if it is fine at "lower RPM" but not at higher. Are you sure
about the accuracy of your Tachometer? If you changed the alternator, it may
not have the same pulley diameter as
the original alternator. The Tachometer on the Perkins Diesel operates off the
alternator. After replacing our alternator, I noticed that the engine seemed
much more efficient. I now would find that our speed was much higher at a lower
RPM. Or so I thought!
I borrowed a flash gun tachometer. It
measures the true RPM of the engine by placing a small piece of reflective tape
on the main pulley of the drive shaft, and a flash gun, linked to a VOM used to
measure true RPM. I discovered that our engine was actually running a full 20%
higher RPM’s than indicated on our tachometer. Thus, rather than the reading of
2,000, it was actually going at 2,400 RPM. 3,000 was
actually 3,600 RPM. This may contribute
to overheating. What prop are you
running?
regards,
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You
certainly touched on a good point when you mentioned tach accuracy. Anytime an alternator is replaced, there is a
good possibility that the new pulley is a slightly different diameter. This
really plays havoc with accurate RPM readings on a Perkins. I used a mechanical
tach right off the crankshaft pulley to calibrate mine. I also had to replace
the original Perkins-supplied tachometer since it had no provision for calibration.
The cruising RPM for your Perkins is
strictly dependent on your transmission ratio. In general, 2:1 ratio's seem to run best between 1800 to 2200 RPM with a
properly sized prop. That RPM range will increase with a 3:1 ratio. Also, the
prop size and pitch will usually be quite different with a 3:1 ratio. One of the more common discussions I've heard
while cruising, is the happy hour, marina comparison of prop size/ pitch/
engine-to-cruising speed and RPM. I remember hearing that "the engine must
be able to reach 3000 RPM underway" and/or "the engine must be able
to reach max RPM underway or the prop is pitched wrong". I have repitched
the prop 3 or 4 times and changed props 2 or 3 times trying to make that
happen. I have had my boat "overpropped" and "under-propped". I finally figured out from a mechanic that
Tayana got it pretty close from the factory and that my Perkins is specifically
designed and rated for the 2:1 transmission that it came with. I use 1800 to 2200 RPM as a good trade off
for speed versus reasonable fuel efficiency.
The performance chart that I posted is only
accurate for a Perkins 4-108 with a
Wayne V-42 C/C RESTLESS April 2001
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It doesn't sound like a problem with the
prop to me. I have a 50-horse Perkins, a BW Velvet drive 1.9:1 and an 18x8 prop
and I can do 3000 in gear. Although maybe your prop is out of
spec. Have it reconditioned.
Ray 2001
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You’re
getting much better performance (rpm) than I do. I’ve been messing around with repitching the prop (can't remember if the current one is
18x11 or 17x12 or if it's one and needs to be the other). I can't get more than 2,000 rpm...but I’m
working on it.
Bill T-37 2001
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Check the FTP site for some info I put up regarding
the Autoprop. It is a fairly complete discussion of props vs. speed (links updated August 2005):
ftp://tognews.com/Perkins_4-108_PerformanceSpecs
I have never
(in 20 years) been able to run my Perkins over about 2400 to 2500 RPM without a
slow rise in temperature. With a
Wayne V-42 C/C RESTLESS
June 2002
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Hi Bill & Doug,
With
my Perkins 4-108, I cruise at 1800 to 2000 RPM. Never
more than 2200 RPM, even when in a hurry. At near 7 knots under power,
the V-42 starts to bury her stern and raise the bow. She will sail at or above
these speeds easily but will not motor at over 6.5 to 6.8 knots without
requiring exponentially greater power settings. I can't see pushing a hull much
above its hull speed. The 33-foot waterline length is the limiting factor.
My max RPM underway is around 2600 with the
Autoprop and was maybe 2700 with a regular 3-blade. I know that many mechanics
recommend that an engine be able to turn 3000 RPM. That may be fine with a 3:1
transmission ratio but it is not feasible with a
Wayne
V-42 C/C RESTLESS
June 2002
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Sirena Originally
had a 18x12 prop and I was unable to get much above
2200RPM but was able to go 7.5 knots. Yanmar said, "You sail-boaters are
always afraid to burn fuel, that engine should be run at 24-2600 rpm with a max
RPM of 2800. You will carbon it up and never reach it's
proper torque HP range. Your prop has to
have some pitch taken out...."
So....I had the prop re-pitched to
18x11.25, can now do 24-2600rpm, but can't get above 6 knots.....So there you
have it from me.....Anyone have a 18x12 prop for sale...............
Charles N. T-37 May 2003
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My boat had the non-standard taper on the
original shaft as well. I changed it when I got a new shaft, then had the hub
of the
Wayne V-42
C/C RESTLESS August 2003
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Prior to having the prop re-pitched, I was
only able to get 2250 RPM under load and max no-load 2500. After the prop was
reworked, I was hitting 25-2650 under load and could do just over 3k no load.
HOWEVER...as I mentioned in an earlier post, my SOG went from 7 to 6
Kts.....And you know that extra knot is a must especially going through
Charles N. T-37 September 2003
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Tad,
Last year we had some discussion on
engines overheating and prop pitch. I had the pitch on mine changed (wish I
could remember what it was before) to 16 x 10 (3-blade). It immediately
increased my cruising RPM’s from about 1800 to about 2500 without overheating.
Boat speed increased slightly. I get
between 6 and 7 knots at 2500 RPM depending on conditions.
I would definitely recommend
re-pitching as it gets the engine running closer to optimum where you get more
of the horsepower out of it. (though I'm still a long
way from the 3500 to 4000 RPM’s for peak horsepower of a Perkins 4-108).
Mark S/V Windbird Tayana
V-42 cc September 2003
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This is a repeat of a frequent discussion
regarding prop size, engine RPM, max power and max speed.
With all the different experiments by
Tayana owners, has anyone gotten the RPM of a Perkins up to 3,000 on a Tayana
37, and how did that affect the boat speed, engine temp, etc. I can understand
the concern about running the engine at prolonged slow speed of 1,000 rpm and
never higher, but if the engine is at 2,000 to 2,200 rpm and pushing the boat
at 6.5 knots in flat water, that seems like decent performance. I also enjoy
lolling about in gentle anchorages and up remote fjords at slow speeds. This
often means rpm ranges of about 1,000 under minimal load (no major seas, no big
currents).
According to the graphs of the Perkins 4-108
on the Tayana ftp site, the torque maximizes at 1,900 - 2,400 rpm. The max
recommended cruising speed is 3,000 rpm. Although horsepower does continue to
increase at higher and higher rpm, I had always been told that the ideal range
of rpm of a diesel engine was in its maximum torque zone. That should also
provide a high enough rpm to help blow off excess carbon, etc.
I also was under the impression that
fuel efficiency drops sharply when you push above about 2,000 rpm with a
reasonably correct prop. Pushing the hull from 5.5 knots to 7 knots can almost
double your fuel consumption of a displacement semifull
keel hull. At 5.5 to 6 knots, we get about 0.6 to 0.7 gallons per hour,
depending upon sea conditions.
I have occasionally pushed to about
3,000 rpm, and got up to 7 knots, but the noise, vibration (even with a
balanced engine and shaft), and fuel consumption bothered me.
In contrast, I have run a Yanmar on a
Hunter 356 at 3,000 for hours, yet only managed about 6.5 knots, but with a two
bladed prop. A recent trip on a 39-foot displacement double ender, similar in
many specs to the Tayana 37, running at 2,000 rpm on a big Cummins diesel, gave
about 6.5 knots with a fuel consumption of more than one gallon an hour.
According to the surveyor (who was a
real turkey), we have an 18x12 prop.
Clean bottom, clean prop.
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I think my prop is not correct; I can only
get up to 1700RPM. A diesel mechanic told me that I was probably overpropped. I've searched the archives to "propeller
pitch" and found no comments that specified pitch, although I remember
seeing them in the past.
I've got a Yanmar 3QM30. Help?
Dean October 2004
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Dean,
No idea if this will help, but we
have a T37 w/ a 3QM30F and a Kanzaki-Hurth
transmission. We just got a new 17" x 9.5" pitch Campbell Sailor prop
(www.westbynorth.com). We're only getting 2100 RPM (should be max 2800). The
manufacturer recommends that we send it back and get it repitched to 8".
Mark Kaynor T-37 October 2004
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Hi Dean...
My Prudence has a Perkins 4.108, with a 17
RH 10 prop. I "cruise" at hull speed at the 1500-1800 range, and
rarely go over 2000.
John Kalpus Prudence
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I took a diesel mechanics course at
Terry told us that you should be able to
run your engine up to its full rated RPM in the slip. If not the boat is over
propped.
He also told us that the unchallenged
leader in causes for diesel engine failures on sailboats is due to the use of
inappropriate plastic vented loops on the raw water line just before it gets
injected into the exhaust system. The tiny holes in the black Marelon vented loops get filled with salt and become
plugged. When that happens the loops don’t vent and a
cooling engine can pull water through the raw water pump and fill the cylinders
with sea water. Onan makes a bronze vented loop with
a flap valve the size of a quarter that eliminates the problem.
John Lewis October 2004
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John,
That seems a bit slow for the Perkins. Does your engine get up to temp (~180). My Perkins will not get to temp until 2800. My Mechanic told me the same thing that was told to John Lewis about max RPM at the dock (actually he said almost MAX RPM, you should be able to hit max RPM while under way. At the dock you are a bit slower since you are getting more resistance from the non-moving water). The MAX RPM for the Perkins is 4000 RPM, so 3600-3800 RPM is about right.
My prop, I think, is a 16" x 17 Right Hand. At 3000 RPM I use almost exactly 1 gal/hr and cruise at about 6.5 knots using a Perkins 4.108.
Regards, Andy T-37 October 2004
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My Perkins doesn't go much above about 2500 RPM, but that may be limited by the pedestal guard, as I can't push the throttle any further, and will have to disassemble it to see if the throttle can be raised further.
If I recall correctly, our prop is an 18x12 3-bladed fixed. We can cruise all day at 2,000 RPM at about 6.5 knots, depending upon wind/waves/current. Our fuel consumption is about 0.6-0.7 gallons per hour. Our overall average is about 10 nautical miles per gallon. Temp hardly ever goes about 170-175 F.
regards,
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I think that I am under propped. I can run at 3000 and above (according to the tach) easily, I usually cruise at 2800, which corresponds to about 6 knots (per the GPS). I intend to measure my prop next haul out.
Speaking about temperature, my Perkins
usually runs just under 180 F. On a recent trip to
Dan Baker T-37 Che Bella October 2004
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Sea Schell has an 18 X 11 3 blade fixed with a 1981 Yanmar 3QM30 that moves her @ 5.5 - 6 knots in flat water.
Harry & Melinda Schell T-37 Sea Schell
May 2005
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When I first got Southern Cross, she had a 17x12 prop, driven by a Yanmar 4JHE. This was definitely too small, but probably the original. At 2600rpm, I got about 5.6kts. The engine would also easily exceed max rpm. I now have an Autoprop, 470-H5 (18.5 inches) and at the same rpm, I get about 6.5kts and it won't over rev anymore.
Paul s/v Southern Cross V-42-cc May 2005
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We have an 18" Max Prop on Magic Dragon. When we bought the boat, the previous owner had decided it was under-propped and had adjusted the pitch up a notch, so we were unable to make more than 3000 RPM with the Yanmar 4JHE. The stern would squat severely and black smoke would boil out of the exhaust at that engine speed.
I repitched the prop back down last year and the engine seems much happier. I don't remember exactly what the exact pitch measurements were/are. They're in my logbook on the boat. I'll look this weekend and report back.
If you are thinking of replacing the prop, I would definitely recommend ponying up the extra $$ and going with the Max Prop or Autoprop. More speed under sail, and greatly improved backing ability.
Frank Timmons V42 Magic Dragon May 2005
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EVOLUTION,
Dick Miller EVOLUTION V-42
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Try Baumann propeller service co., 713
926-6908,
Dan May 2005