More than 12 HP on my O'Day 30'?

[Meis]

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.

 

[Justin_NSA]

Practical Sailor has an O'day 30 review that includes your engine and how it's mounted. Worth a read

O'Day 30 - Practical Sailor

Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.

www.practical-sailor.com

 

[sail sfbay]

The attached Practical Sailor article talks about the engine hp from early O'Day 30's of 12 hp and then 16 hp. Understand later models may have installed a Universal 18 hp engine based on one O'Day 30 sailboat data site. I came across the article below that provides a formula for calculating motor hp (for outboats) for sailboats as a function of displacement hp = displacement / 550. That is closely confirmed by the Cruisers Forum thread below. Some O'Day 30 owners in this forum will likely offer their engine motor hp recommendation and experience.

O'Day 30 - Practical Sailor

Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.

www.practical-sailor.com

How to Calculate Outboard Motor Size for Sailboats https://www.cruisersforum.com/forums/f55/engine-size-1577.html

 

[Tally Ho]

My O’Day 322 (10,000 pounds IIRC) has a Yanmar 2GM20F 2-cyl. I think the engine is rated about 16HP.
I find it to be sufficient in most conditions. I am on Lake Michigan, so no tides or river currents to deal with.

Greg

 

[dlochner]

Talk to the engine manufacturers, especially Beta Marine. If the engine is over sized it will not run at an optimal speed for longevity. The top speed of the boat is limited by the theoretical hull speed which is determined by the waterline length and hull form. Trying to exceed hull speed just wastes dead dinosaurs.

 

[Justin_NSA]

If you were to install a more powerful engine, would your old '78 then meet those future needs you mention? Would a newer boat already set up properly be better suited for the long run? Draft? Accommodations?

 

[dmax]

Later model Catalina 30's, similar in size to your boat, came with 21-23HP Universal diesels - I had a 23 HP version with a 3 blade prop, felt like the right amount of power and didn't leave me wanting for more. My current boat has a 21 HP Universal with a 2 blade prop and it too has enough power. With a 30 foot boat, 5.5 - 6 knots is all you can expect as a cruising speed.

 

[JohnShannon]

Well the rule of thumb according to the internet is 1hp for every 500 pounds that puts you at 24 hp. If you want to go faster you need a bigger motor.

 

[rgranger]

Talk to the engine manufacturers, especially Beta Marine. If the engine is over sized it will not run at an optimal speed for longevity. The top speed of the boat is limited by the theoretical hull speed which is determined by the waterline length and hull form. Trying to exceed hull speed just wastes dead dinosaurs.

I think 3 kts is about half hull speed for a 30'

 

[rgranger]

If you were to install a more powerful engine, would your old '78 then meet those future needs you mention? Would a newer boat already set up properly be better suited for the long run? Draft? Accommodations?

@Justin_NSA makes a good point. Would the cost of a repower be about the same (maybe more) than selling your boat and buying one that already has what you need and want? I guess it is hard to answer that question without doing some market searching... and we all know how much sailors hate looking at boat ads

 

[dlochner]

Well the rule of thumb according to the internet is 1hp for every 500 pounds that puts you at 24 hp. If you want to go faster you need a bigger motor.

A bigger motor in a bigger boat. Hull speed is the limiting factor.

 

[odaydokay]

I

I think 3 kts is about half hull speed for a 30'

don';t think O'Day built any boats that would only do 3 knots, so I suspect his engine is not just right performance-wise. My 28 has 10HP (M12 Uni) and she can make 5.5 knots I estimate. I guess I would assure myself the current mill is doing its job, rather than throwing the baby out with the boat water (sorry!)

 

[Roland5048]

Replaced the original YSB-12 in my '77 Hunter 30, (10,000 lb displacement), with a new 3YM20, (21 hp), 12 years ago. I had already owned her for ten years and knew I was going to keep her. Pricey but well worth it in the long run. I did not want to rehab another old boat. I can easily cruise at 6-6.5 knots at 3/4 rpm. Difference is like night and day. That was my situation, then. Yours may be totally different.

 

[dlochner]

Replaced the original YSB-12 in my '77 Hunter 30, (10,000 lb displacement), with a new 3YM20, (21 hp), 12 years ago. I had already owned her for ten years and knew I was going to keep her. Pricey but well worth it in the long run. I did not want to rehab another old boat. I can easily cruise at 6-6.5 knots at 3/4 rpm. Difference is like night and day. That was my situation, then. Yours may be totally different.

As a rough guide, at 80% of WOT the boat should go close to hull speed in light to moderate conditions. If it takes more power, then the engine is too small, prop pitch wrong, or the engine needs servicing.

If the boat reaches hull speed at much less than 80% then the boat is probably overpowered.

 

[FastOlson]

That OEM Yanmar YSM-12 (?) was a great engine. If your boat is motoring less than 5.5 knots, something is really wrong with your prop size or pitch.
Our 10600# 1988 boat came with a Universal 23 hp three cylinder and I replaced it in 2018 with a Betamarine 25. We were motoring at 7.0 before the change, and we still are. Gotta say, the newer-design Beta (Kubota short block) is a lot quieter all around.

OTOH, if you want a smaller and easier-to-fit replacement, the Betamarina 20 is a well regarded three cylinder engine also.
As for the inevitable discussion over whether to sell the whole boat and start over.... if your present boat is the right boat for your needs for another decade, and the rest of the boat is well maintained... repower and be happy.

Fair winds!

 

[Davidasailor26]

I

don';t think O'Day built any boats that would only do 3 knots, so I suspect his engine is not just right performance-wise. My 28 has 10HP (M12 Uni) and she can make 5.5 knots I estimate. I guess I would assure myself the current mill is doing its job, rather than throwing the baby out with the boat water (sorry!)

That was my thought too. We could do 6 with a clean bottom on our 28 without being WOT. 3 knots sounds like something else is afoot. Sounds like the speed is low with 2 different props, so I assume it’s not prop pitch or fouling. Maybe engine issues, or inaccurate speed measurement from a paddle wheel transducer?

 

[Justin_NSA]

Have you checked against a GPS?

 

[Benny17441]

We had a 12,000 lbs. boat with an 18HP Auxilliary Diesel and the best we could do under motor alone was 4.5 Knots. So I would not doubt your assertion. If it was not for the sails we would not have gotten out of some situations where we were pushing one knot at WOT. Some boat builders take the definition of "auxilliary engine" quite literally. If you navigate rivers I would repower with a 25 HP engine.

 

[JohnShannon]

Hull speed is 1.34*sqrt(LWL) per sailboat data the LWL is 25 so hull speed is maybe about 6.5 knots. If he is motoring at 3 knots and he has already changed the prop and I presume has a clean bottom he is underpowered. The rule of thumb suggests 24 hp 12 is for sure too low. My 4500 lb 30 ft boat does 6kn under motor with 9hp but it is light and has low windage. In any case 500 lbs per HP puts me at 9 HP.

The cost of a reposer is likely to be substantial probably better off just buying a different boat. On the other hand if we apply rational thought and economic analysis to sailing we wouldn't

 

[FastOlson]

Do not underestimate the power in the YSM12. I have done a 5 day delivery on a 33 footer with that same engine, and it can push a sailboat @ 6 kts.
The OP really needs to check on the prop and boat bottom. The stated speed is far below reasonable expectations.