sunray ss-165

[ISLAND_HOPPER]

Well i want to start off, im new to the forum but am not new to browsing through the many threads and posts to usuly fined what i need to know. this time however i come up empty handed. my brother and i just bought a sunray and i believe it is an ss165, 15.4' with a mecuary 115 l6. it has a 19 pitch prop on it and well the boat just dosent seam to work well at all. it is sketchy through the watter at a fair clip. it wants to dart around allot. also from a dead stop when you pin the throttle the boat seams to wined up but wont get out of the hole. she just sticks her nose in the air even with it fully trimmed down, it will level out and sit good in the watter after a min but it should just jump. guess what i am asking is what can we do to stabelise this boat out at higher speeds and what can we do to get it out of the hole. if anyone has any info on these boats i would be verry happy.

[KnottyBuoyz]

Take some of the pitch out of the prop
Look for added weight in the boat that wasn't originally there.
Add trim tabs

[ISLAND_HOPPER]

there is another thing, someone had put a bracket between the motor and the transem to what looks like to rais it uo and down. when you are going along alot of watter comes up from there and coming into the boat. it looks like it was put there to adjust for depth of the engine in the watter.i wonder if we take it off if it will help any, i am going to take pictures and post them up to show the setup that is on the boat.

we took out the sand bags that were in the front, and it has been lightend. and what do you mean by trim tabs?

[KnottyBuoyz]

Trim tabs are devices mounted to the transom of your boat that you can use to control the trim of the boat without adding weight.

http://www.bennetttrimtabs.com/tabsdo.htm

[ISLAND_HOPPER]

that sounds like it would help out alot, i wonder if it would help with our problem of our prop slipping in the watter at wot when you back of just a little it seams to stop spinning.

[KnottyBuoyz]

Originally Posted by ISLAND_HOPPER

that sounds like it would help out alot, i wonder if it would help with our problem of our prop slipping in the watter at wot when you back of just a little it seams to stop spinning.

Others will correct me if I'm wrong but I think you're experiencing cavitation from the overpitched prop. At WOT it's producing bubbles from the trailing edge of the blades and the prop begins to spin in the bubbles and that's probably the slip you're experiencing. Dialing in the correct prop can sometimes be an educational experience. If you've got a good prop shop or dealer nearby they may have a set of test props you can try.

[ISLAND_HOPPER]

well i know i have read about cavatation before when i was looking at toying with surface drives but this would be the first time to ever experience it first hand. is there any formulas out that might give a ruff idea of the correct prop size and pitch or is this all just gonna be hit or miss

[KnottyBuoyz]

Originally Posted by ISLAND_HOPPER

well i know i have read about cavatation before when i was looking at toying with surface drives but this would be the first time to ever experience it first hand. is there any formulas out that might give a ruff idea of the correct prop size and pitch or is this all just gonna be hit or miss

If you can find the service manual for your engine it'll specify WOT RPM. If you can get to the specified RPM w/o it slipping then you're probably pitched correctly. If you can't get to the spec'd RPM, say 200 or more RPM less then you have too much pitch. Going down 1" in pitch usually raises the RPM about 200. So if you're 400 RPM short of spec at WOT you'd need to put on a prop with 2" less pitch. It'll only put you in the right ballpark.

[ISLAND_HOPPER]

wow looks like we are in for some fun. thanks allot for all of your help, im going to try the trim tabs and going to try the prop as well to see if we cant get this thing figured out. i hope to have pics of the boat up soon and how bad someone has hacked it up as well. its not a pretty sight but we hope it will be allot of fun. thanks again

[KnottyBuoyz]

Feel free to add some reputation points! *wink*

Cheers! BTW I have a Sunray too, 1987 Mirage, 25', Volvo Penta AQ271A (GM 350 @ 270 HP) and a VP Duoprop outdrive. It took me three yrs to dial in the correct props so I know where you're coming from.

[ISLAND_HOPPER]

oh god i can see i am in for alot of fun lol. all this info is def worth some rep