Hi!

I've got an interesting problem. The 10.5hp diesel engine in my
28footer sailboat only pushes at about 3.5knots cruising speed at
around 3600rpm, which is the max. RPM that is recommended for the
engine.

I ruled out the following problems:
- The engine HPs are theoretically sufficient for that boat (drag/
displacement vs. hp). According to calculations I should get up to
7knots (I'd be happy with 6).
- The engine compression is as good as it should be.
- The hull is as smooth as it gets.
- The 3 blade propeller is in like new condition and exactely the one
that is spec'ed for the boat. I had that verified and measured by the
propeller manufacturer and several other people.
- The engine revs easily above 4200rpm (tried that very briefly). It
revs that high either in forward gear, in reverse gear or in neutral.
- The RPM gauge shows the correct RPMs. When doing 3600 RPMs, the
engine definetly feels like doing 3600 RPMs.
- I recently had the shaft coupling, the shaft itself, the shaft seal
and the cutlass bearing replaced. They are brand new. The problem was
the same before and after the replacement.

To summarize: the engine has plenty of power (high rpm in gear), the
prop is ok, the hull is ok, the shaft is ok.

Therefore, the only problems which I could imagine a
1. The transmission clutches slip either due to overuse/age or due to
misadjusted shifting lever.
2. Because this is a custom built boat, the transmission is not the
right one and it has the wrong gear ratio.
I can't really easily figure out 2. So I first tackle 1.

The engine has been running like that at least for 50h now and I would
imagine the problem to get worse, if the clutches were slipping. But
it stays the same so far. Also, I do not notice unsteady engine revs.
It's reving nice and stable and there's no jumping, which I would
imagine would happen if the clutches would not "bite" properly.

Did anyone ever have a problem with slipping clutches in a sailboat
transmission? And what were the symptoms? Did the engine have very
unsteady rpms and "jumped"?

Any advice is appreciated.

Cheers,
Dennis

On 1 Feb 2007 16:53:35 -0800, "Dennis"
wrote:

Hi!

I've got an interesting problem. The 10.5hp diesel engine in my
28footer sailboat only pushes at about 3.5knots cruising speed at
around 3600rpm, which is the max. RPM that is recommended for the
engine.

I ruled out the following problems:
- The engine HPs are theoretically sufficient for that boat (drag/
displacement vs. hp). According to calculations I should get up to
7knots (I'd be happy with 6).
- The engine compression is as good as it should be.
- The hull is as smooth as it gets.
- The 3 blade propeller is in like new condition and exactely the one
that is spec'ed for the boat. I had that verified and measured by the
propeller manufacturer and several other people.
- The engine revs easily above 4200rpm (tried that very briefly). It
revs that high either in forward gear, in reverse gear or in neutral.
- The RPM gauge shows the correct RPMs. When doing 3600 RPMs, the
engine definetly feels like doing 3600 RPMs.
- I recently had the shaft coupling, the shaft itself, the shaft seal
and the cutlass bearing replaced. They are brand new. The problem was
the same before and after the replacement.

To summarize: the engine has plenty of power (high rpm in gear), the
prop is ok, the hull is ok, the shaft is ok.

Therefore, the only problems which I could imagine a
1. The transmission clutches slip either due to overuse/age or due to
misadjusted shifting lever.
2. Because this is a custom built boat, the transmission is not the
right one and it has the wrong gear ratio.
I can't really easily figure out 2. So I first tackle 1.

The engine has been running like that at least for 50h now and I would
imagine the problem to get worse, if the clutches were slipping. But
it stays the same so far. Also, I do not notice unsteady engine revs.
It's reving nice and stable and there's no jumping, which I would
imagine would happen if the clutches would not "bite" properly.

Did anyone ever have a problem with slipping clutches in a sailboat
transmission? And what were the symptoms? Did the engine have very
unsteady rpms and "jumped"?

A slipping transmission is definitely one possibility.

Also possible is a wrong reduction gear ratio, possibly because of
forward and reverse gears reversed, or possibly it was incorrectly
specified.

Last but not least, the propellor may have incorrect pitch, or
diameter/blade area may be too small causing excessive slip through
the water. That's not likely with a three bladed prop however.

Is your speed log calibrated? Do you see higher speeds under sail?

"Dennis" wrote in message
oups.com...
Hi!

I've got an interesting problem. The 10.5hp diesel engine in my
28footer sailboat only pushes at about 3.5knots cruising speed at
around 3600rpm, which is the max. RPM that is recommended for the
engine.

I ruled out the following problems:
- The engine HPs are theoretically sufficient for that boat (drag/
displacement vs. hp). According to calculations I should get up to
7knots (I'd be happy with 6).
- The engine compression is as good as it should be.
- The hull is as smooth as it gets.
- The 3 blade propeller is in like new condition and exactely the one
that is spec'ed for the boat. I had that verified and measured by the
propeller manufacturer and several other people.
- The engine revs easily above 4200rpm (tried that very briefly). It
revs that high either in forward gear, in reverse gear or in neutral.
- The RPM gauge shows the correct RPMs. When doing 3600 RPMs, the
engine definetly feels like doing 3600 RPMs.
- I recently had the shaft coupling, the shaft itself, the shaft seal
and the cutlass bearing replaced. They are brand new. The problem was
the same before and after the replacement.

To summarize: the engine has plenty of power (high rpm in gear), the
prop is ok, the hull is ok, the shaft is ok.

Therefore, the only problems which I could imagine a
1. The transmission clutches slip either due to overuse/age or due to
misadjusted shifting lever.
2. Because this is a custom built boat, the transmission is not the
right one and it has the wrong gear ratio.
I can't really easily figure out 2. So I first tackle 1.

The engine has been running like that at least for 50h now and I would
imagine the problem to get worse, if the clutches were slipping. But
it stays the same so far. Also, I do not notice unsteady engine revs.
It's reving nice and stable and there's no jumping, which I would
imagine would happen if the clutches would not "bite" properly.

Did anyone ever have a problem with slipping clutches in a sailboat
transmission? And what were the symptoms? Did the engine have very
unsteady rpms and "jumped"?

Any advice is appreciated.

Cheers,
Dennis

"Hobbs" wrote in message
...
Is your speed log calibrated? Do you see higher speeds under sail?

"Dennis" wrote in message
oups.com...
Hi!

I've got an interesting problem. The 10.5hp diesel engine in my
28footer sailboat only pushes at about 3.5knots cruising speed at
around 3600rpm, which is the max. RPM that is recommended for the
engine.

I ruled out the following problems:
- The engine HPs are theoretically sufficient for that boat (drag/
displacement vs. hp). According to calculations I should get up to
7knots (I'd be happy with 6).
- The engine compression is as good as it should be.
- The hull is as smooth as it gets.
- The 3 blade propeller is in like new condition and exactely the one
that is spec'ed for the boat. I had that verified and measured by the
propeller manufacturer and several other people.
- The engine revs easily above 4200rpm (tried that very briefly). It
revs that high either in forward gear, in reverse gear or in neutral.
- The RPM gauge shows the correct RPMs. When doing 3600 RPMs, the
engine definetly feels like doing 3600 RPMs.
- I recently had the shaft coupling, the shaft itself, the shaft seal
and the cutlass bearing replaced. They are brand new. The problem was
the same before and after the replacement.

To summarize: the engine has plenty of power (high rpm in gear), the
prop is ok, the hull is ok, the shaft is ok.

Therefore, the only problems which I could imagine a
1. The transmission clutches slip either due to overuse/age or due to
misadjusted shifting lever.
2. Because this is a custom built boat, the transmission is not the
right one and it has the wrong gear ratio.
I can't really easily figure out 2. So I first tackle 1.

The engine has been running like that at least for 50h now and I would
imagine the problem to get worse, if the clutches were slipping. But
it stays the same so far. Also, I do not notice unsteady engine revs.
It's reving nice and stable and there's no jumping, which I would
imagine would happen if the clutches would not "bite" properly.

Did anyone ever have a problem with slipping clutches in a sailboat
transmission? And what were the symptoms? Did the engine have very
unsteady rpms and "jumped"?

Any advice is appreciated.

Cheers,
Dennis




If the transmission is slipping it would get hot. Run it in gear and feel
the transmission. Get a strobe tack and measure actual engine RPM's vs
shaft RPM's. There should be a reduction ratio on a tag on the
transmission. There should also be a model number.

Since a slipping clutch would get worse until it totally slips I would guess
that the pitch is off on the prop. Did you check the pitch?

Did someone put the prop on backwards when they repacked your shaft? It
could happen.

Bill Longyard

In article .com,
"Dennis" wrote:

I've got an interesting problem. The 10.5hp diesel engine in my
28footer sailboat only pushes at about 3.5knots cruising speed at
around 3600rpm, which is the max. RPM that is recommended for the
engine.

We have a fairly modern Yanmar. We use an effective 5-6 HP to drive us
along at 5+ knots. At idle, we move at about 3 knots.

I believe your prop is under-sized. I would increase diameter to the max
your boat can accommodate before considering pitch, then max that out.


--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's NEW Pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

On Thu, 01 Feb 2007 16:53:35 -0800, Dennis wrote:

Hi!

I've got an interesting problem. The 10.5hp diesel engine in my
28footer sailboat only pushes at about 3.5knots cruising speed at
around 3600rpm, which is the max. RPM that is recommended for the
engine.


Do I understand that the 3600rpm is NOT at WOT (wide open throttle)? If
that's the case, you're definitely underpropped (or slipping).

I did have transmission-slippage problems, and they were quite similar to
what you're describing. Iirc my problem was actually the linkage: the
transmission wasn't getting fully into gear.

But I suspect the prop size. "recommended by the mfr" is rarely the
correct prop, especially if the transmission ratio is not standard (and
if you have a tapered shaft like virtually all inboards, you can't put the
prop on backwards!) I find the easiest way to mess with prop sizes is buy
a second prop, get the pitch you THINK is right and put it on. Then, after
you've used that for a while, get the first one re-pitched to what you NOW
think is correct, and put it on. And so on. You will finally end up with
the correct prop on, and a spare (that you can repitch to also be correct).
Sounds to me like you need AT LEAST another inch of pitch, maybe two. I
donno about diameter: a 10hp engine can't swing a very big prop, esp. a
3-blade. Maybe 12-14inches, tops?

Your pitch is correct when you're getting 3600rpm at WOT under way.

druid - has a 14x8 3-blade Campbell Sailor on Far Cove (26hp)
http://www.bcboatnet.org