outboard size for a sailboat

[parito]

Sail drive propeller will give you better thrust (don't ask me to explain why though). Are you measuring speed through the water rather than SOG? If you're doing 5.4 over the ground into a Thames tide, you're doing well.

Nicola

I am measuring speed through the water.

 

[maxcampbell]

4HP long shaft; 21' LOD (about 17'6" LWL); 650Kg displacement. We kept up with a Centaur coming out of the Colne into 20 knots of wind against tide on Saturday - despite crashing & banging, and occasional screaming as the prop came out of the water. I reckon the 4HP just about does it, 6HP would be lovely.

 

[John the kiwi]

The 10 HP Honda is a smaller engine than the 15hp (222cc vs 350cc ) I think you will find although only about 4.5 kg lighter.

A 9.8 hp Tohatsu is about 9.5 kg lighter than the Honda 15 hp ... That's about 20% lighter

Thanks for that. When i compare options and leg lengths it seems Tohatsu 9.8 is about 7 .5 kg lighter than my current 15 Hp honda on a like to like basis.
Even so it is a significant weight saving, and is a better option than i had found when i last compared.
Must write a letter to Santa and reform my ways....
Thanks and regards