yamaha 115 2 stroke + propeller

[timddo]

i have a newyamaha 115 2 stroke but am confused with propella. Wot is 5500 and speed is only 33 knots. 13*17pitch propella. I've been reading the yamaha performance chards at the speed should be around 39 knots. So if i change to 19 pitch, will that make the difference????.

The boat is cavitating a little so i will lower the motor one hole. Cavitation when i did steep turn. Will this increase or decrease speed.

[FNQCairns]

Tim looks like a fishing rig, base your cavitation on how well it holds in the lumpy stuff, a little cav on tight turns is OK unless you ski with it. Going down a hole will slow it down and use more fuel + extra wear n tear, no advantages unless it airates too much in the lumps.

Sounds close to OK that doesn't mean you couldn't find another couple of knots with a different prop but they are expensive.

You could consider getting the cup knocked out of that standard yam prop, would probably help you a little.

Are the ones you are comparing it to the same prop? is yours 13dia or 13 something diameter?

cheers fnq

[whiteman]

I got 35 out of mine (5500) on Saturday in glass with not much fuel on board. It pushes a 5.3 Quinnie. Not much control at that speed.

[ozscott]

mate - not sure what my SS prop is on my 93 115 Yammy 2 stroke, but I get a comfortable top speed of 35-36knots at WOT (about 5700rpm) on my 21foot 70s Seafarer Vagabond.

[3Vs]

I get about 39 knots in flat conditions in my Rum Runner II

[MyEscape]

Ozscott

what sort of weight is your boat? Is your speed measured by GPS?

Probably sounds like I'm doubting you as I have a 5 metre Cruisecraft with a 115 Merc and it pushes around 36knots at 5500revs. I just ask as I was thinking your hull must weigh significantly more than mine.

Steve