Hello, I have been working on my 37c that has yet to go into the water since I bought it. It was originally Jolly Roger in Melbourne Florida. Anyway, I am in Green Cove Springs North Florida and almost immediately upon putting her in the water I must get to Brevard County. The boat is equipped with the 3qm30 and a three-blade prop. I'm wondering what a reasonable cruising speed is so I can plot fuel and time. I don't want to run it as fast as possible but I don't want four knots either. Can someone give me a reasonable idea, not pushing the motor too hard, what kind of speed I should be able to make in calm water? Thanks much!
37c motoring speed
- Thread starter Cocoa Beach Sailor
- Start date
On my old H37 with a 3QM30 and a two-blade Michigan Wheel prop, I used to make about 6.5 knots at approximately 2200 RPM. That seemed to be the sweet spot for me. Speed went down by up to a knot with opposing wind and seas or a dirty bottom.
Agree with Jim. My experience is 7 statute miles per hour at less than 0.7 gallons of diesel per hour.
if you are going to motor “hard” for some hours on end it is essential to ensure that the raw water system is in good shape. This is intake strainer pump heat exchanger exhaust manifold and mixing elbow.
if you are going to motor “hard” for some hours on end it is essential to ensure that the raw water system is in good shape. This is intake strainer pump heat exchanger exhaust manifold and mixing elbow.
Thanks much! I was planning on 6.5 statute miles per hour with a brand new clean bottom and little to no wind. Hopefully it will be windy and I can shut the silly motor off and go out offshore and sail down but as a backup I've got to figure out my motoring situation. It is been Dead Calm for 4 days. It would really be irritating to have to motor 150 Mi or so after having put so much time and money into this boat! One other question, assume a beam reach, what kind of wind speeds would I need to hit six and a half miles per hour or I guess that would be 5 and 3/4 knots or so. Assume stretched out sales that someone who can trim pretty decently, not a pathological string puller but pretty close
I forget where I am on that subject. I have read so many different things about the subject. Unfortunately most people talk about what engine they have, which is not relevant. It is about the transmission. I have a zf45-1 which I believe is better left in reverse.
Neutral is never a bad decision. Some transmissions tolerate reverse, and your Hurth might be among them, but that’s more drag than neutral anyway.
On the subject of not wanting to push the engine too hard - most marine diesels recommend running around 80% of full power continuously. Counterintuitively running them too gently causes more problems by allowing carbon buildup instead of keeping everything hot enough to stay clean.
Hull speed (square root of DWL x 1.35). If you can’t make hull speed under power you’re underpowered. About 7.5 with a 31-ft waterline (if that’s right for H37).
That said, has anyone with an auxiliary sailboat ever complained about having TOO MUCH available power? Ever? Anyone?
That said, has anyone with an auxiliary sailboat ever complained about having TOO MUCH available power? Ever? Anyone?
If the boat is not making close to hull speed in calm water with no wind or current, then the engine might be too small or it might not be correctly pitched or sized.
Over powering a sailboat is bad for the engine. Diesels want to run at about 80% of WOT. If the engine is over sized it will run at a much lower rpm causing problems with glazing on the cylinder walls and carbon build up in the exhaust.
Probably not, but plenty have complained about poor access around the engine, which can be a little better with a smaller block.
Well; I meant all things being equal. There’s not much difference in size between a Yanmar 8 and a Yanmar 10; so, so long is WEIGHT - which I think is the biggest concern - is within the same range, there’s no reason to go smaller in power.
My dad was completing Antigone, our Raider 33, and looking into the Radio Shack catalogue he called me over and said, ‘You know about these things. What’s better: a little stereo working hard or a big stereo hardly working?’
I swear it’s the only time I remember him asking me for advice. So I answered him the way he’d have answered me. ‘What do YOU think?’
He thought about it and then said, ‘A big stereo hardly working,’
So I said what he’d have said: ‘Rrrright.’
He bought the little stereo because it was cheaper. And then bought the best aluminum speakers they had. That’s how he was.
(The stereo is still in the boat.)
I’ve always heard it’s best to run a diesel at pretty low RPM, so long as it’s under load. 80% of WOT means nothing to me if I don’t know the revs. On our 44 the diesel (which at 33 HP was too small) ran at 900-1200 pretty much all the time. Pathfinder introduced a VW/Audi 5-cylinder marine diesel that ran more like double that. We weren’t impressed with the longevity estimates.
I don’t think it’s essential that you DO run at hull speed all the time; but the point is that you CAN. The boat is designed to operate at hull speed 24/7, even well into degrading conditions. If you’re struggling up swells against the wind (which most electric-powered boats do, and badly) it’s vital to have that extra power on hand.
It’s the same as with driving. Sometimes the accelerator is your friend. Even your lifesaver.
The engine's manual should indicate what the max RPM is, take 80% of that number. Or, on a calm day with flat water, run the boat with the throttle wide open, to see what the rpms are, take 80% of that number. If the manual's rpm is significantly different from the max rpm obtained on the water the prop is not pitched correctly.