Outboard motor sizing for a sailboat?

Question

I have a 30 foot long sailboat that weighs in at 11,000 lbs. It's old inboard 10 hp motor is bad. I would like to mount a 10 hp long shaft (25'') on the transom. I keep getting different advise, some say go to a bigger 20 hp motor while others claim the lighter 10 hp is ok. Use of the motor is to get in and out of bays and slips, in coastal waters. I'm not that interested in speed nor going back to an expensive inboard, and most running time would be a hour or less. Thoughts?

Answer 1

Whichever hp you choose, make sure the propeller is sized properly for the job. Diameter and pitch need to be corrected for more thrust not top speed on a heavy 5.5 ton load. A four blade may even be recommended.

Another thing to consider is how heavy the engine is because you will be taking it on and off every time you use the boat so no one steals the engine. Four stroke engines are generally heavier.

Answer 2

as for the docking engine i would stay within 20 horsepower  i would think that  a 15 would do the trick.  

Answer 3

Your not the first person to confront this problem.  I know you'll not like my advise but read it anyway.  See if you can find a replacement for the inboard.  There are a lot of clever solutions I've seen.  Like a battery driven, "bow thruster" type hydraulic motor or an rebuilt Atomic-4.  If you must go outboard, go smaller than your thinking.  I've used the Merc 7.5 and Evinrude 6 HP.  You have to get the "sailboat prop" but they are available.  Keep in mind that it will take a lot longer to get moving and more importantly longer to slow down, but they will get the job done, in fact better than a 20 or 35 hp.  I don't know why other than its gear ratio and prop pitch and max rpm that you can use without cavitation.  Good luck!!!1

Answer 4

If you are going new- I would get a 4 stroke from Honda. Their 10 horse is bullet proof. The 15 is OK but lots more weight for the 5 horse power. The 15 is a 3 cylinder. Mounting may be a problem. Make sure it won't sit out of the water when you run forward. Carry spares as some places just give you a blank look when you ask for honda parts.

Answer 5

Generally too much horsepower is used. If the existing 10 HP, stay with that size. More HP = MORE WEIGHT, MORE $$$