finding prop for a 16' glastron trihull with 85hp Johnson 1977

[Devonaaron]

I have a 16 foot glastron v16 stinger aqua lift. I have a 85hp johnson I have this big thick heavy cast prop no idea what its made out of some kind of iron or steel mixed with other alloys to prevent rust and corrosion. This was a random prop this guy gave me with the motor I think its to big and to high pitched for my boat. My question is I am going to be island hopping with this boat in the inter coastal water ways in FL going about 20-35 miles round trip and I need a prop where I can reach a good RPM that wont suck gas but will at leased take me 30MPH so i can get where i need at a reasonable pace. Do you think I should go with a 4 blade from what im reading im guessing I need something about a 17" pitch but I just rebuild them and fix them I have a good idea what I need but I dont have a tach on this motor due to its age and problem with finding a tach that will work off the voltage, But I juts ordered a tiny tach. Thank you so much keep in mind this is a very strong motor, good spark 130 compression carbs rebuilt everything perfect. I need to tune the low idle a bit but that will just take some tools and a day out on the water by myself. Im anxious to hear some ideas thank you

 

[steelespike]

Re: finding prop for a 16' glastron trihull with 85hp Johnson 1977

There are probably others that can be more accurate than me;
without prop size ,rpm and speed a prop is an educated guess.
A 12 3/4" X 17" 4 blade Solas Amita prop should work.It may be less than what you need but your better off with less than too much.If too much prop you shouldn't use it If too light you can reduce throttle to avoid over reving.If you get the Tinytach I mentioned in your other post you can tell if the 17 is it.The Solas Amita has proven to be predictable and reasonable.

 

[Devonaaron]

Re: finding prop for a 16' glastron trihull with 85hp Johnson 1977

Im unsure if I need a 4 blade im traveling long distances in choppy water on a smaller boat any opinions or ideas ?

 

[steelespike]

Re: finding prop for a 16' glastron trihull with 85hp Johnson 1977

Long distances in choppy water and from your original post wanting to cruise
at about 30 the 4 blade will help handling,help the boat maintain plane at reduced speed making it easier to handle chop.Some sort of trim tabs may help as well.
though agressive use of tabs can reduce top speed.
The tri hull isn't likely to do as well in chop as a deep V or other softer chined boats.