prop help?

[ratking20]

after a lot of work done to my boat the last 2 years im ready to shop for a new prop

i have a 22 foot sea ray 220 bowrider... 350 mercruiser efi 5.7

i did alot of work on the boat including new stringers, foam and deck. so the boats weight may have changed. i also dropped a new to me engine in. went from carb to efi, same size 350 5.7.

first i know my prop is dinged up pretty bad. i had her out today and at wot she was at 4000(i think that is a lil low)
and it seems slower now than with the old tired engine i had. today at wot she was only doing about 28(gps) mph at 4000rpm
both seem low to me. i know the prop is bad, thats why im here. what should i be doing now.

could the bad prop effect the top speed by that much(5-10 mph)???? im going to find out the exact size of my current prop in the morning.

can someone point me in the right direction??

 

[steelespike]

Re: prop help?

We'll need your prop size(near base of the blades or under the prop nut),hopefully your gear ratio off the out drive.The motor is probably rated for 4800 rpm.
I would think a 5.7 could run around 50 with a light load.

 

[ratking20]

Re: prop help?

ok so i removed the old banged up prop. cant read the numbers off it, but i believe its a 14x19 aluminum

so the 14 x 19 alum(bad condition) had me at 26 mph(gps) and 4000 rpm wot
i borowed a ss rop from the boatyard to see the difference
its a 13.88 x 23 stainless and it had me topped out at 27 mph and 3400 rpm wot

i couldnt read the numbers off the outdrive to find out the gear ratio
the boat didnt plane out too fast and after it did it took a bit to actually get to top speed
my tachometer could be off, but i think i should be goin g alot faster
any help would be great.........thanks

 

[ratking20]

Re: prop help?

i looked up on the sea ray website. my outdrive should have had a 1.50 gear ratio and lists a 4600 rpm wot

 

[agallant80]

Re: prop help?

If its a 5.7MPI then the WOT should be 4,800-5200
MerCruiser 5.0L, 350 MAG & 377 MAG | Mercury Marine

As for the prop try this:
Prop Selector | Mercury Marine

Also from what I have noticed is that props can only take so much damage. When I had an aluminium prop if I dinnged it the slightest the top end speed, pickup were all effected.

 

[ratking20]

Re: prop help?

the prop selector only has options for engines years 2000 and up
and the gear ratio that i have is not listed if i try a different year

 

[ratking20]

Re: prop help?

anyone?

 

[steelespike]

Re: prop help?

At 26 mph 4000 rpm I think you have more issues than a prop.
If we assume you need to be at 4800 you would need to drop to a 15" pitch.
that's close to what you n might use on a big pontoon boat.You have a motor that lists props up to 28"
and your boat is pretty much what you might find a 5.7 making 50 mph.
A 15" pitch would produce about 40 mph at 4800, a 19" would produce about 50 at 4800.
To compare, a 3.0 in a 19 footer would produce about 38-40 at about 4800 with a 19"
Assuming the hull hasn't lost its form we have to consider the motor/drive system.
Check that the throttle opens all the way, confirm its running on all cylinders.Do a compression test.
Perhaps a bad injector or a failed coil assuming individual coils per cylinder.
Perhaps the initial timing is set wrong?
Its not a stretch to say your running at 1/2 speed at 26 mph.