OB size for 28' 8,000 pound sailboat

[pvanv]

I have an 8,000-pound sailboat that uses a small outboard for aux power, and I need to replace the motor. This is a long shaft, remote control, electric start setup, in a lazarette well.

Originally, this was an anemic 9.5hp 2-stroke. Everyone has replaced them with bigger motors. We now have an old Evinrude 15hp (similar to a 9.9), which is adequate. Definitely not too big for the boat.

I would like to buy a 4-stroke Tohatsu. But what size? The 4-stroke 15 is a lot heavier, which is an issue, getting the motor in and out of the well. Also, the 4-strokes have a much larger cowl -- just look huge compared to the old 2- strokes.

Some dealers have told me that the 4-strokes have much better low end power than the old 2-strokes, and so the 9.8 has such good low end thrust that it would be fine. Others say that I need 1hp per 500 pounds of sailboat, so a 15 is proper. But I'm not convinced one way or the other yet.

Since price is about the same for the 9.8 and 15, what do you think? The new 15 is 20 cubic inches, while the 9.8 is 12. The old 15 was 15 cubic inches.

So do I go with the 9.8 or the 15?

 

[steelespike]

Re: OB size for 28' 8,000 pound sailboat

I have to wonder about a 4 stroke having better low end power than a 2 stroke.The 74 up E/J 2 stroke 15 is only 13 cu. in. obviously much smaller than the 20 cube.Perehaps that helps. I think the critical point is thrust/prop bite at maneuvering speed.Are you getting a dedicated high thrust motor meant for auxillery application.Most any motor could push your boat at speed
with the right prop, but slow speed control is the key in my opinion.

 

[pvanv]

Re: OB size for 28' 8,000 pound sailboat

Agreed that the top end isn't really the question, except powering to weather. The current E/J 15 can give me near hull speed in flat water. Would be using as low a pitch (6 inches or so) prop as possible. I don't think the Tohatsu 15 has a High Thrust aux prop as does Yamaha. Yes, slow speed control and reserve power is what I'm after. The 15 is a huge weight penalty. But is does have twice the alternator, which might be nice.

 

[TOHATSU GURU]

Re: OB size for 28' 8,000 pound sailboat

You need a 18 or 20 hp. A 15 would be find for forward thrust, but in reverse you will need more.

 

[pvanv]

Re: OB size for 28' 8,000 pound sailboat

Thanks to all who have posted.

I have determined that the 15 will not physically fit through the lazarette hatch, so the only option is the 9.8 with high thrust prop.

 

[eipeldau]

Re: OB size for 28' 8,000 pound sailboat

Hello,

I have a 20hp Honda installed on the transom of my 27', 7500lbs sailboat. It is long-shaft and has a high-thrust, 4x10x6.5 propeller. It has lots of thrust in both forward and reverse. I can reach hull speed (6.2kts) at around 4000rpm and the maximum speed is 6.7kts at 5400rpm. I cruise at 5.5kts(3500rpm) and at such speed I spend 0.45gal/h. It's also got a 12A alternator, which is very useful on a sailboat. If you have room for it in your lazarette, I'd recommend it to you.

Henrique