Will a 9.9 hp be adequate for a 12,000 pounder? - SailNet Community

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  #1  
Old 02-26-2011
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Will a 9.9 hp be adequate for a 12,000 pounder?

I have a 33' 12,000 pound sailboat with an atomic 4 inboard motor. It was rebuilt 8 years ago and runs good for the most part. Every now and then it wont start at a bad time and I had a line snag on the prop that immobilized me until I dove to cut it lose. I decided to have a backup outboard put on and got a 4 stroke yamaha 20 horsepower - I understand the limitations but in calm sheltered harbors and marinas I think it will be good to have for docking maneuvers etc. Anyway the guy I had install the bracket put it about as low as he could and the prop is barely touching the water. Its the long shaft (20") version and yamaha doesn't make a longer version.

I am down to either trying to some how make the bracket reach lower or selling the Yamaha and getting a 25" shaft outboard. From my research I can only find 9.9 hp outboards with 25" shafts. Would a 10hp be useless for a 12,000 pound hull? The inboard is 30hp and I rarely need all its got - I figured the 20 would be an adequate backup but am not sure about 10...

Another reason I really want to have the backup outboard is I detest trying to access the atomic 4 on my hands and knees due to injuries I have that make such work very uncomfortable...
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Old 02-26-2011
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We lost our engine (broken timing belt) on a cruise once with an 16,000 lb 40 footer, about 3 days from home. When we couldn't actually sail we strapped the inflatable alongside and in calm conditions could make about 3 knots with a 5 hp outboard on the dinghy. So 9.9 should move you fine, keeping in mind that for long trips with a risk of chop it will be less ideal, and the fuel consumption may be more than your A4.

If all you need it for is marina exit and entry as long as there isn't enough sea to render the O/B useless regardless of HP then I'm sure it will be fine.

This would be even more true if all you need it for is the occasional backup if/when your A4 fails.
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Old 02-26-2011
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I hope they beefed up the transom where the outboard bracket is mounted, since you're dealing with some serious forces there, and the transom wasn't designed to handle them originally. If not, you should do so before relying on the outboard for any distance.

A 9.9 should move your boat, but you'll want to get a high-thrust prop for it, since most outboards aren't propped for a heavy displacement load like a keel sailboat.

Be aware that being transom mounted, the outboard is far more likely to ventilate as the boat rocks in heavier seas. It will not be very useful except in relatively calm conditions.
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Old 02-26-2011
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The big limitation to using a kicker will be stopping power should you need it. It will NOT stop your boat quickly. 10 hp will move the boat along just fine, I would guess you could motor in forward at upwards of 6 knots. For comparison, I have a 9.8 hp kicker on a 28' 10,000+lb commercial crab boat and it will push it along at 5 knots if calm. As you have discovered keeping the prop in the water is difficult, if not impossible, in all but flat calm conditions. I don't know what type of mount you had made for the outboard, whether it is fixed or raises and lowers, but if it is fixed you might look into a Garelick kicker bracket that raises and lowers. They make them that have up to 15" of travel. If one of these would get the prop in the water you could keep your 20 hp.
http://www.defender.com/product.jsp?path=-1|294|314561&id=524175
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Depends on how much windage your boat has. In calm
water a 9.9 would probably be OK for backup. The most
important thing is getting the prop deep enough. Also,
I think getting the "high thrust" prop option would be
beneficial. No matter how much HP you have, it won't do
much good if the prop comes out of the water when it
gets rough.

Dabnis
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The transom had 4 1/4" starboard (synthetic marine ply) layers and a steel plate sandwiched between the bracket and the hull but the actual glass itself was not modified - are you saying extra fiberglass should be laid on to the original hull to thicken it?

So there might not be a huge difference between a 10 and 20 hp 4 stroke considering I would only consider it useful for calm conditions and mostly for maneuvering.

Will look into the high thrust prop was surprised to see the 20hp had a prop not much bigger then my dinghy's 4hp 4 stroke...
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I have a garelick bracket that raises and lowers but it only lowers to perpendicular to the transom so a longer arm will in effect raise the motor higher from the water. (Please enlighten me if I'm missing something as I'd love to somehow turn the bracket upside down or something am scratching my head how to make this work without having to sell the brand new motor and possibly get a new mount as well) Another thing is that it is extremely difficult to raise the motor once its lowered have tried winching it with my spinnaker halyard with little success.
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Can you post a picture of what you've got?
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Quote:
Originally Posted by Mariner777 View Post
The transom had 4 1/4" starboard (synthetic marine ply) layers and a steel plate sandwiched between the bracket and the hull but the actual glass itself was not modified - are you saying extra fiberglass should be laid on to the original hull to thicken it?
Yes, the transom itself should be strengthened or reinforced to spread the load of the outboard and transfer it to the hull. BTW, starboard is not a structural material, and really shouldn't be used in high-load situations. In most cases, the transom is reinforced by glassing in 3/4" plywood and at least four or five additional layers of glass all the way across the width and tying the transom into the hull.

Quote:
So there might not be a huge difference between a 10 and 20 hp 4 stroke considering I would only consider it useful for calm conditions and mostly for maneuvering.

Will look into the high thrust prop was surprised to see the 20hp had a prop not much bigger then my dinghy's 4hp 4 stroke...
The high thrust prop will usually be a larger diameter and a shallower pitch than the normal prop.
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Mariner,
Not sure, but I think Honda, maybe others make a "sailboat
special" motor with extra long shaft, different gear ratio, and
large diameter, low pitch prop. It may be possible that a 9.9HP
version of this motor could deliver similar thrust as a 20-HP
standard prop motor with a shorter shaft, and weigh less?

Dabnis
20HP
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