In article .com,
"Dennis" wrote:

I've got a 28 foot sailboat, 7800lbs with a 10.5hp engine. It has a 3
blade prop with 10 inch diameter and 9.3 pitch. Prop is in like new
condition, so is the bottom. When I sail, I can push her up to 6 knots.

Though, when I spin the engine at 3600 rpm I only get about 3.5 knots
out of the boat. The engine easily manages more than 4000 rpm, so I
don't think it's an engine problem. I suspect that the prop has the
wrong pitch, but according to the manufacturer it's exactely the right
one.

Why don't I get more than 3.5 knots under power? Does anyone have a
similar configuration or any clues?

Entirely depends upon which engine and transmission you're using, but
that seems off.

We're a nominal 6800# running a Yanmar 2GM20, and our prop (16x10x3)
allows us my target RPMs, 3400, but we normally cruise at about 5 hp
output (0.3 GPH and 22-2300 rpm), doing about 5.5 knots.

If I changed the pitch, I could pull about 3800 before the governor
kicked in, but I prefer to max out at our continuous rating.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/