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Old 13-07-2020, 06:53   #1
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1978 O'Day under-powered with 12HP Yanmar?

Most sailors don't like to talk about adding HP to their boat, however as we begin another stage in our lives, we are looking at more ease in movement via motor. Our 1978 30' O'Day weighs 12,000 lbs and has always been considered under-powered with the 12 Horse Yanmar (3 knots top speed in good conditions). My question goes out to anyone who has replaced an engine in that type of boat as to how many horses I should bump up to if replacing the Yanmar 12. Some have mentioned 25 HP, while others have suggested electric (a bit expensive to retrofit, and early in it's use). Last year I went from a two blade prop to a three blade. Gave me some quick bursts, but only increased drive minimally. Again, we are looking for power for longer motoring and a slightly higher rate of speed, with the power to face a thunderstorm if necessary, or to push myself through some silt on the river bottoms in our travels. Any advice will be welcomed.
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Old 13-07-2020, 15:18   #2
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Re: 1978 O'Day under-powered with 12HP Yanmar?

Whilst I don't know your O'Day 30 ( nice looking boat ) 3 knts seems way slow for it's design & a 12hp. E.g. we have an 8hp single Yanmar in a 26ft sloop & we can cruise at 4.5knts.
Sounds like your engine is worn out if you have the right prop.

A berth neighbour has a 20hp 3 cylinder kubota in a sistership & can do 7knts.

Having said that yes you would be better off with a 25hp ( I'd recommend Beta or at least a Kubota base engine ) if you want to do more motoring.
You could probably get away with a 20hp but you would be working it harder so I'd agree with those that said 25hp
Maybe someone with your design will chime in or google to see if there is an O'Day owners association.
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Old 13-07-2020, 16:20   #3
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Re: 1978 O'Day under-powered with 12HP Yanmar?

Not to be a smart arse, but I’d put in what would fit, or sell the boat. It’s likely a lot of money to spend on a 42 yr old 30’ boat.
I would want a three cyl myself, an in-line 6 is the best balanced smoothest running, but a three isn’t bad, better than a twin or a four.

Add in the cost of a folding or feathering prop and driveshaft and maybe shaft log etc. I say folder or feathering because it’s going to be a lot larger and therefore more drag if it’s not, and your current shaft and even exhaust system may not be large enough.
Could get real expensive.
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Old 13-07-2020, 18:30   #4
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Re: 1978 O'Day under-powered with 12HP Yanmar?

Yes A64 has a good point,
You could well get another boat with a near new engine for much less than the cost of a re-power. I know how attached people can get to their current vessel however.
But I wanted to post something from another thread about a 12 hp Yanmar in a similar length boat so you can see what speed you should be getting. Note he was only getting 5.5knts before rebuild. I'm assuming your speed is from a GPS.
Don't know what particular Yanmar you have but the 12hp singles are easily rebuildable. Anyway here is the post:

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Re: Yanmar SB12 Using Oil
The boat got launched Monday the 5th. I've not gotten the mast stepped yet, but hope to do so tomorrow, and so I've not really motored the boat very far - just the mile to the club from the launching ramp and a couple of runs from the mooring to the dock.

The motor is running very well. It is smoother than I remember and it starts on the very first compression cycle. The knot-very-accurate meter shows 6kn at 2700 rpm and 6.5kn at 3000. I think that is a bit faster than it has been before. I won't claim any increase in speed until I can fully check things out with a GPS. (It seems to me that at any given RPM it shouldn't be any faster than before.) I have no report on the oil consumption yet - I've not even checked it - but I will start monitoring it as soon as I start putting some real time on the engine. There are no obvious oil leaks or other problems.

I'm hopeful this old motor is ready for another forty years!
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Old 14-07-2020, 08:49   #5
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Re: 1978 O'Day under-powered with 12HP Yanmar?

Quote:
Originally Posted by jmmeis View Post
Most sailors don't like to talk about adding HP to their boat, however as we begin another stage in our lives, we are looking at more ease in movement via motor. Our 1978 30' O'Day weighs 12,000 lbs and has always been considered under-powered with the 12 Horse Yanmar (3 knots top speed in good conditions). My question goes out to anyone who has replaced an engine in that type of boat as to how many horses I should bump up to if replacing the Yanmar 12. Some have mentioned 25 HP, while others have suggested electric (a bit expensive to retrofit, and early in it's use). Last year I went from a two blade prop to a three blade. Gave me some quick bursts, but only increased drive minimally. Again, we are looking for power for longer motoring and a slightly higher rate of speed, with the power to face a thunderstorm if necessary, or to push myself through some silt on the river bottoms in our travels. Any advice will be welcomed.

My Watkins 29 weighs in at around 10,000 lbs...and Ive got a Yanmar 2gm20F. At 2500 RPM Im getting close to 6kts. Are you sure you have the right prop on your boat? Is the prop and bottom clean? Compared to an O'day, my boat is like a bus... you should be getting more speed.
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Old 14-07-2020, 08:50   #6
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Re: 1978 O'Day under-powered with 12HP Yanmar?

My Newport 30 had a 9.9 diesel and did 5 knots. One difference is I boat on the west coast and the tides are something to consider. I would be in A64's train of thought to get what you can put in. You didn't mention if the motor is a 1978, but newer diesels have reduced weight per horsepower. Good luck.
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Old 14-07-2020, 08:52   #7
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Re: 1978 O'Day under-powered with 12HP Yanmar?

Try a different prop?

We had a Beta 30 in a 30' 14Klb displacement boat and it worked well. Love the Beta engine and re-powered our current boat with a Beta 85.
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Old 14-07-2020, 09:05   #8
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Re: 1978 O'Day under-powered with 12HP Yanmar?

I have to jump on the bandwagon wrt how much to invest in this boat. Though they are wonderful boats. We chartered one for a week when our two kids were 6 and 10. We had a great time on it.



Anyway, another great source of advice would be a dealer in your area or starting with one of their websites. For example, https://betamarine.co.uk/engine-selection-for-yachts/


Dealers might have a bead on one to rebuild that is coming out of another boat.
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Old 14-07-2020, 10:29   #9
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Re: 1978 O'Day under-powered with 12HP Yanmar?

jmmeis:

The power you need to achieve "hull speed" (and a bit) in any sailboat of conventional design is determined by "rule of thumb" (actually as a matter of empirical observations over many, many years) as 2HP per ton displacement if all you use the engine for is going in and out of your marina. 3HP per ton if you "motorsail" frequently under conditions of wind and wave that don't seem too onerous, and 4 HP/ton if you have to buck weather of some significance.

You are 12K, you say, so that is 6 ton (near enuff), and your HP requirement is therefore something between 12HP [which is what you have, and now you know why it feels wimpy :-)] and 24HP. Given the minimal cost difference between engines of 12 HP and 25HP, there is NO sense in being stingy with the power installed. Installation costs are the same whatever you install. A 25HP Beta would be my choice. I have a 20HP Beta on a nominal displacement of 9K lbs, so I'm probably 12K lbs laden. I do just fine in the Salish Sea.

You also need to have regard to the propeller through which the engine's HP is transmitted to the water. The diameter, just off the top of my head, would have to be 16" for a 25HP engine in your boat, and the Pitch would probably be 14". You can find propeller calculators on the Web. Find one, and play with it just to get a "feel" for what these parameters "should" be.

O/Bs suffice for nothing more than going in and out of marinas. They are, and always have been, a make-shift arrangement in a cruising sailboat.

Forget about "electrifying" your boat. On her displacement she won't carry the weight of batteries required for any serious cruising/motoring.

TrentePieds has a waterline length of 25 feet, so her "hull speed" is 5 * 1.35 = 6 3/4 knots. Yours is gonna be just about the same. With 25HP and the right prop you'll get 6 knots through the water the greatest part of the time. If you are pounding in a 30knot headwind and a 3 foot slop, you might not get all of that, but in those conditions you are likely gonna fall off and go home anyway :-).

Cheers

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Old 14-07-2020, 10:37   #10
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Re: 1978 O'Day under-powered with 12HP Yanmar?

I'd want the 25 hp rated motor, or at least about an actual 20 at a reasonable rpm.
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Old 14-07-2020, 11:01   #11
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Re: 1978 O'Day under-powered with 12HP Yanmar?

When I got my Pearson 30 it had a blown engine ( atomic four ). I scoured the country on Craig's list and found a Yanmar 3GM30F on the other side of the country. Shipping was no big deal.

After all, is said and done. I have replaced everything from the prop to the engine. The prop matches the engine perfectly and I never have to worry about being pushed around by the current. I love having the power and feel comfortable taking the boat anywhere.

It was not hard to replace the engine, I made some custom mounts ( had to go narrower )and bolted it up. I have 56 hours on it now and it never misses a beat. We have tested it in some strong conditions and it is really nice to know that I have extra juice if I need it.

If you have a Yanmar now it should be an easy swap. Just make sure you get a prop that is matched. To me, it was worth the money. Also for fun, I can punch it from a standstill and the boat jumps.
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Old 14-07-2020, 11:02   #12
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Re: 1978 O'Day under-powered with 12HP Yanmar?

Thank you for all of the recommendations. This gives me many different things to consider, and places to start looking. One thing I have known since I started sailing some 52 years ago is that sailors are extremely helpful and thorough!
You have not let me down! Safe sailing everyone, and thank you again for your input!
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Old 14-07-2020, 13:34   #13
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Re: 1978 O'Day under-powered with 12HP Yanmar?

As far as I can remember, the O'Day 30 is quite heavy(10000 Pounds), but its underwater profile is very modern and fast. So, 3 knots for a 12 HP is very low, and I believe that you have a problem somewhere as long as your knotmeter is not lying, of course!... Propeller pitch or diameter, Engine mechanical problem, or serious fouled under belly, or propeller. With some logical approch(Check maximum RPM, and specs for your present propeller, and compare it with another For a Yanmar 12 hp). First, be sure to have a clean bottom and propeller and start trouble shouting: You need an RPM attached to your engine, an essential tool!. At full throttle, If the engine Rpm is too high, it may indicate a too small prop or too little pitch. If on the contrary, the engine can't reach is designed Rpm, the prop is probably in cause or the engine's timing is wrong( rare occurence is this small engine). You should be able to go close to twice that speed and certainly cruise a 5 knots, in flat waters. So don't despair or spend a lot of money and time... And have fun!
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Old 14-07-2020, 13:47   #14
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Re: 1978 O'Day under-powered with 12HP Yanmar?

I can't speak to a 30. A 27, circa 78, with 10hp was under powered with any current or tide running. A nice boat however , well made.
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Old 14-07-2020, 14:05   #15
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Re: 1978 O'Day under-powered with 12HP Yanmar?

Quote:
Originally Posted by Elie View Post
As far as I can remember, the O'Day 30 is quite heavy(10000 Pounds), but its underwater profile is very modern and fast. So, 3 knots for a 12 HP is very low, and I believe that you have a problem somewhere as long as your knotmeter is not lying, of course!... Propeller pitch or diameter, Engine mechanical problem, or serious fouled under belly, or propeller. With some logical approch(Check maximum RPM, and specs for your present propeller, and compare it with another For a Yanmar 12 hp). First, be sure to have a clean bottom and propeller and start trouble shouting: You need an RPM attached to your engine, an essential tool!. At full throttle, If the engine Rpm is too high, it may indicate a too small prop or too little pitch. If on the contrary, the engine can't reach is designed Rpm, the prop is probably in cause or the engine's timing is wrong( rare occurence is this small engine). You should be able to go close to twice that speed and certainly cruise a 5 knots, in flat waters. So don't despair or spend a lot of money and time... And have fun!
Yes, although generally under powered, pitch, clean bottom and reaching max rpm will be important. The boat should do a lot more than 3 knots even with the 12Hp. Most 30 foot lighter boats should do 5 knots even with a 10HP outboard.
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