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Catalina/Capri 25/250 Sailor's Forums

Catalina 250 Specific Forum

Yanmar sail drive

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rgreno
Deckhand

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Canada
3 Posts

Initially Posted - 08/06/2011 : 07:59:09

I have a c250 with a 9hp yanmar operating at 2300rpm hull spd is only around 3.2 knt I can't seem to get to hull spd? Am I running too low rpm what kind of spd should I expect? Any help is appreciated.

Edited by - on

John Russell
Master Marine Consultant

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USA
3444 Posts

Response Posted - 08/06/2011 : 08:15:17

Roberrt,

Welcome to the forum.

Unfortunately, you'll find that very few Yanmar Saildrive versions exist. In fact, this is the first I've seen a posting about one here.

I might want to look at the condition of the prop if the motor seems to be running normally. Is it covered (like mine gets sometimes) with plant life? Is it fouled with some fishing line or the remnants of something that was submerged?

My 9.8 Tohatsu outboard can easily get to 4.5+ knots or more with less than half throttle. Is 2300 rpm as much as it will turn? I've never even attempted to achieve hull speed (~6.18 knots for our boats).

BTW, multiple postings with the same question tends to confuse and dilute the responses. I'd suggest deleting the question in the other sections of the forum.

Edited by - on

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 08/06/2011 : 08:32:22

Concur about the multiple postings and the Tohatsu performance. We can hit about 4.5-5 kts at about 1400 rpm. That's with a freshly cleaned & painted hull. Your boat is capable of attaining roughly 6-6.5 kts maximum speed. Can you go anywhere near that speed while sailing?

If not, have you seen the boat out of the water, or dove to take a look at the hull? You might have marine growth that's slowing you down. I'd check that as well as John's suggestions about prop fouling.

Edited by - delliottg on 08/06/2011 08:35:43

britinusa
Web Editor

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USA
5404 Posts

Response Posted - 08/06/2011 : 09:14:56

Is that hull speed or GPS speed?

We recently passed through Ceasar Creek from the ocean into Biscayne bay. GPS speed was around 2+ knots, hull speed (speed through water) was 5+ knots!

Paul

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Stinkpotter
Master Marine Consultant

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Djibouti
9081 Posts

Response Posted - 08/06/2011 : 10:27:00

First, let's check terminology... "Hull speed" is generally considered to be the theoretical maximum speed a boat can achieve without lifting its bow over the bow wave. The simple formula is 1.34 * sqr(length at the waterline in feet), which is about 6.2 knots for the C-250. Under power, that tends to be an inefficient speed--the engine works too hard--so most of us only go 5 - 5.5 knots maximum for a smooth, efficient ride.

The comments on hull and prop condition are valid... Your 9 hp. should be sufficient to get above 5 knots if you have the right prop that will let it reach the right RPMs for efficient power delivery (which varies by engine and is quite different for a diesel versus the gas engines most of us have). If your prop pitch is too great, it won't let the engine get to its sweet-spot RPMs... and 2300 seems low to me--check your Yanmar manual. I would think you should be operating in the upper 2000 range, for power and for "smoothness" (especially with one cylinder), but I don't know the Yanmar 1GM10 specifically.

Are you not able to get higher RPMs?

(By the way, you can delete your duplicate threads if you get them before somebody replies to them.)

Edited by - Stinkpotter on 08/06/2011 13:33:28

mhartong
Navigator

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USA
152 Posts

Response Posted - 08/06/2011 : 13:49:21

Persephone has a Yanmar sail drive (1GM10-SD20) with the standard fix blade prop that comes with the saildrive. I am assuming that you have the same set up.

At 3600 rpm (the maximum operating speed) you will generate roughly 9 HP at the crank shaft, propeller shaft and at the propeller. Operating at 2300 rpm you will only be generating about 5 HP at crank shaft, and around 2 HP at the propeller (much less efficient). Your speed of around 3.2 to 3.5 knots at 2300 rpm is very consistent with what I have seen (with a clean prop I can do about 3.5 knots). Considering the size of a C250 that is pretty respectable given the actual effective HP.

Running at 3400 rpm (maximum sustained operating speed), I am able to make just a little over 5 knots, I don't run the engine faster than 3400 rpm unless I REALLY have to. While the engine is cable of 3600 rpm, it is a 1 hour rating. I usually run around 3200 to 3300- which gives me around 4.2 to 4.5 knots.

There is the trade off of speed for fuel consumption, At 2300 rpm you should see your fuel consumption around 0.2 gallons per hour compared to roughly 0.5 gallon per hour at 3400 rpm.

Keeping a clean prop is very important. You will be surprised what just a few critters who decide to take up residence on your prop can do to your speed.

If you have a variable or folding prop you will also see a slight drop in speed for a given horsepower rating compared to a fixed blade prop under power. But in that case you are trading speed under power for speed under sail. You are also looking at additional cost and complexity with either a variable and folding prop. If you are looking to get every last bit of speed under sail, then you probably would want to swap your fixed blade prop out.

While having the prop continuously in the water does allow for increased marine growth, its still awfully nice if you get any sort of wave action- you don't have to worry about it coming out of the water like an outboard might. It's also another 230 pounds down low, and on the centerline, which helps with stability. Plus, there is the esthetic's too- nothing hanging off the back end of the boat.

Mark

Edited by - mhartong on 08/07/2011 05:09:55

At Ease
Admiral

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672 Posts

Response Posted - 08/06/2011 : 14:14:22

Sorry, didn't realize we had dual threads here on the same topic. Here's what I just posted on the other thread...my boat is an inboard, not a sail drive:

Your hull speed is 1.34 X the square root of your water line length. That speed should be attainable at 80% of WOT (wide open throttle). My 27 hp Yanmar's WOT is 3,600, so I get hull speed around 2,800 RPM. With a water line length of 28', the hull speed for my boat is 7.1.

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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.