ten or eleven three or four?

[novakm]

Hoping for some prop advice. I have a Lund Impact aluminum sport/fish boat. It's 16'9"long, 90"beam, 76" chine. It has a Merc 60 EFI 4 strake for power, with a 10.63 x 12 prop at 1:1.83

Mostly it's used for fishing with one or two guys. For this it works great. Top speed 32mph at 6,000rpm. I find I need to trim up a little to get max speed, and when I do, the prop can pull in some air in turns.

I also use it for family. With a full load of 4 adults and 2 small kids, it has a very hard time getting on plane. Sometimes it can't get on plane at all. Once it's on plane, I still get 29-30MPH at about 5,700 rpm. I'd also like to pull a tube. Kids are small, and I'd probably only pull them at 15mph. Thier dad is bigger, and he would like to go more like 25.

Boat weighs 1125lbs, and I probably add another 1,000 lbs in people, fuel, and stuff. I'm thinking to use my current prop for fishing, and change it out when I go on family outings.

Should I go down to a 10 pitch, or would this cut top speed too much for pulling the dad? Would 11 be enough of a difference that I could get on plane reliably? 4 blade or 3?

I'm also wondering if smart tabs would be a better solution than a smaller prop. I'm just afraid that with a light load they would cause the bow to drop too much.

Any suggestions would be appreciated.

 

[Ccfbailey]

Re: ten or eleven three or four?

I'm going through kinda the same thing. I think if you're rpm is 6000 with that prop, it's going to go higher with a smaller pitch. I doubt your motor should rev higher than 6. I'm new to this and I'm sure others will be more help. I have a merc 90hp 4stroke and its rated for 6000rpm. It's going up to 6200 currently with a 15p. I'm going to try a 17p to bring up the speed and bring down the rpm. It's fun to experiment, huh?

 

[novakm]

Re: ten or eleven three or four?

Cc,

6000 is a little high. I'd go to a bigger prop if it would get on plane easier!

 

[steelespike]

Re: ten or eleven three or four?

When adding smart tabs you need to add just enough pressure to improve hole shot.
Check the performance tests at the Merc site. They do a lot of testing with their Spitfire 4 blade 13"
on boats your size. Hole shot seems a little slow about 7 sec. to 20, 14 sec. to 30 I assume a light load.
4 strokes have a reputation for struggling out of the hole.
I think the Merc spitfire 4 bld. in an 11" might get you up better and may pull around 6000 wot.
Its not unusual to have to trim down for corners though a 4 blade may help.
The Solas props have a reputation for good predictable performance at less money than the Spitfire.
Solas props are state of the art technology.
I wouldn't hesitate to try an 11" Solas 4 blade.