looking to replace my prop but.....

[dmoriarty51]

when i look it up here by motor and pitch i dont get anything close in size to whats on now.

boat is a 1995 crestliner pro am 1650sc, it has a johnson 70 on it. the prop according to the info stamped on the hub is #389948 13 3/8 x 17

if i look here on iboats for a replacement i get nothing in a 13 inch diameter at all when looking at 17 pitch so perhaps it doesnt belong on this motor?

it seemed to perform ok, i believe i was maxed out near 5000k rpm but cant recall for certain. i plan to run it again with this prop and double check now that i have replaced some worn out spark plugs and and dirty fuel filter.

my average load would be between 5-600lbs what should i be using for a prop? im looking at replacing due to it being rather beat up.

im not chasing 1-2 mph i got the rig on the cheap to learn whether i really want to own a boat or not and its uses include cruising maybe a tube and prolly some fishing

 

[steelespike]

Re: looking to replace my prop but.....

Do some test runs and get us the details.Max rpm and speed by gps is best.
You should be shooting for about 6,000 rpm.Don't worry about diameter if its intended for your motor the diameter will be right.

 

[dmoriarty51]

Re: looking to replace my prop but.....

i'll see what i can do about some test runs, i dont own a gps and i know the speedo on the boat is unreliable. unfortunately i may not find time untill the weekend, and finding flat water on the mississippi on a weekend in this area is a challenge

in the meantime based on what i am seeing listed for this motor, the current prop is oversized?

any decent low dollar gps units to suggest?

 

[dmoriarty51]

Re: looking to replace my prop but.....

its been a long time since i started this but i finally have some info.....

turning 5200rpm on flat water, trimmed out to what felt best and just back in from hearing ventilation, at 32-35mph on the boat speedo, and that felt pretty accurate based on the wind in my face.

my mechanic that rebuilt the motor suggested that WOT rpm was where he would prefer it to be....

so heres what i would like to hear about, 3 blade vs 4 blade. will a 4 blade sized to acheive similar WOT rpm help get me on plane at lower speeds? as it sits right now, im at 4000rpmto plane with just me in the boat... bear in mind the boat is carrying an extra layer of 3/4in plywood on the floor and presumably some wet foam under the floor.....if the floor was bad enough to need replaced/covered i would be shocked to find all the foam dry.

my fall, winter project is to remedy this situation and get the boat back to or closer to factory weight. perhaps i should wait untill i do that and mess with props after seeing how it performs then?

 

[steelespike]

Re: looking to replace my prop but.....

Your boat has a dry weight of 990,motor about 250lbs.You could weigh the boat/trailer subtract the trailer to check for water weight. If the floor needed replacement likely the stringers would too and if not done or done poorly the bottom would be wavy or have a hook.If I replaced a floor I sure as he-- wouldn't leave wet foam.If the boat responds to trim it likely has good hull form.
If motor is a 95 my info indicates a max rpm of 6,000 and the hp is rated at 5,500.
If you run lower your not even reaching your max hp.Of course if freshly rebuilt a break in period is necessary.
If you had a lot of water in the foam your hole shot would be poor.
Check your setup.The antivent plate(just above the prop) should be visable on plane.Check that the throttle opens all the way at the carb.Raising the motor could increase speed and rpm.A 4 blade would allow maximum height with resistance to venting.
A 17" prop is in the ball park,speed may be a little low at 35.
A 3 blade prop gives good overall performance with good top end.A 4 blade give better low to mid range performance with a little better control on plane and at the dock.Top end is usually less.2 to 3 mph.

 

[dmoriarty51]

Re: looking to replace my prop but.....

this is an aluminum boat, so i presume it to not have wood stringers that could have rotted, and the floor wasnt replaced it was floored over, so there are 2 layers down

i would like it to plane a lower rpm, and yeah the motor is pretty fresh yet and is running richer than it probably needs to at this point.

i do plan to weigh the boat, before and after the interior reconstruction

i presume this single axle yacht club roller trailer is maybe 500lbs? i believe the model number is r1718

the boat also has a 28 gallon fuel tank so that adds alot of weight as well, it was probably 3/4 full during that run. so add ~150lbs i weigh 250....

anyways i will revisit changing props in the spring after i see if i can get this thing a bit lighter