prop issue 115 etec

[BUU]

have a 15 '3" carabean comaro(fibreglass) with a 115 hp etec.
Currently have a 13 7/8 dia SST 19 deg pitch and want to pull bigger skiers out a bit easier and was wondering what prop to use.
Tried my old prop off old evenrude 100 which was a SST 13 inch dia with 19deg pitch and with vent holes which I was told would do the trick. It got me off the mark a little better but then cavitated a lot when puting skier out on tight whip.
Boat slowed to almost stop and engine revved to 4.5 k note with both props engine was trimed down.

Any ideas as I was recomended a 18 deg pitched Raker which also has vent holes. I assume it would do the same get me off the mark better but would still cavitate on hard turns.

Currently pulls 52 MPH at 5.7k revs

 

[Bondo]

Re: prop issue 115 etec

have a 15 '3" carabean comaro(fibreglass) with a 115 hp etec.
Currently have a 13 7/8 dia SST 19 deg pitch and want to pull bigger skiers out a bit easier and was wondering what prop to use.
Tried my old prop off old evenrude 100 which was a SST 13 inch dia with 19deg pitch and with vent holes which I was told would do the trick. It got me off the mark a little better but then cavitated a lot when puting skier out on tight whip.
Boat slowed to almost stop and engine revved to 4.5 k note with both props engine was trimed down.

Any ideas as I was recomended a 18 deg pitched Raker which also has vent holes. I assume it would do the same get me off the mark better but would still cavitate on hard turns.

Currently pulls 52 MPH at 5.7k revs

Ayuh,... Welcome Aboard,.... I'd think goin' to a 18" pitch or a 17" pitch might do what ya want...

My main point is, props are measured in Inches of pitch, Not degrees...

 

[jestor68]

Re: prop issue 115 etec

Your situation is not unusual. Many of us use two different props; one for normal operation, and one for serious skiing.

Your best bet would be to get a Solas 17 pitch 4 blade prop for your serious skiing. Do not use a "vented" prop for ski pulling. It actually introduces exhaust gases into the propeller stream, causing ventilation.

If you are turning 5700 rpm with the SSP 19, the 4 blade 17 should run right at 6000 rpm at WOT, which is your upper limit.

 

[steelespike]

Re: prop issue 115 etec

Just incidentally you can't get 52 mph at 5700 rpm with a 19" prop.assuming your gear ratio is 2.00.
Is your speed by gps?Some cell phones have a gps app.
A 19" prop theoretically will move 19" forward in one revolution.
But there is some slip in a liquid so movement is less. slip is measured
as a percent. 10% being reasonable and could be higher or lower depending on the prop and the load.
If we use 10% slip we get about 46 mph. from your numbers.

 

[aerobat]

Re: prop issue 115 etec

i cannot say specifically on a 115 etec but my last boat had an 150 evinrude ficht ram with a 14/1/2X20 vented raker stainless and was good as hell.

never had blow out issues and the modified V6 ficht had a punch on the holeshot i will never forget.

on the other hand - when you top out at 5700 rpm your prop seems to be right and you have to accept what you can expect from a 115 etec and what not.

cheers

 

[BUU]

Re: prop issue 115 etec

Just incidentally you can't get 52 mph at 5700 rpm with a 19" prop.assuming your gear ratio is 2.00.
Is your speed by gps?Some cell phones have a gps app.
A 19" prop theoretically will move 19" forward in one revolution.
But there is some slip in a liquid so movement is less. slip is measured
as a percent. 10% being reasonable and could be higher or lower depending on the prop and the load.
If we use 10% slip we get about 46 mph. from your numbers.

Thanks for your input the speed & revs were measured with the speedo and tacho supplied with motor ,with 2 people in boat

 

[steelespike]

Re: prop issue 115 etec

If you want to do a run with a gps and remind us of the rpm and speed it will help to figure out where the error might be.
While it isn't likely if it turns out you are actually doing 52 then rpm might be significantly higher.We allready know that your slip can't be low enough to make 52.I am inclined to think the speedo is not accurate but suppose its a combination of the 2 gauges.

 

[BUU]

Re: prop issue 115 etec

If you want to do a run with a gps and remind us of the rpm and speed it will help to figure out where the error might be.
While it isn't likely if it turns out you are actually doing 52 then rpm might be significantly higher.We allready know that your slip can't be low enough to make 52.I am inclined to think the speedo is not accurate but suppose its a combination of the 2 gauges.

Thanks , Your probably right, Im looking at borrowing a 19" Viper and see what it does. then if no Joy try an 18" & 17". Either way looks like Ill end up with 3 props,but at least Il get what I want