Prop performance Q...

[frustratedboater]

Greetings,
I have a Mastercraft American Skier with a 13 x 13, three blade prop on it that gives me about 42 mph @ 4000-4100 RPM. I had purchased a 13 x 16, four blade prop and would like to know what the difference in preformance it will give me. Will I sacrifice top end speed if I switch?

 

[hwsiii]

Re: Prop performance Q...

Frustrated, welcome to Iboats prop forum and we will try to help you as much as we can, but there is certain information that is needed in order to help you. When we get information in bits and pieces we are continually having to look back and forth to try and piece the information together. The following form has all of the information that is needed to help you with your problems in finding the right prop. If you do not know all of the information that is asked for on the form please give us the most information you have available as I have a program I designed to find the right prop for any planing hull boat that needs this information, and most other people who are trying to help you will need the same information. It requires time to find all this information when we have to look for it and in my defense I expect you to be willing to expend as much effort in finding the right prop as I do. We hope to be able to help you get the exact prop you need for your particular uses, and this information is required to do that.
It is not as simple to pick the right prop as most people coming to this forum think it is, that is why we ask so many questions, it is for your benefit we ask all these questions. And if you have a stainless steel prop or are changing to one the blade geometry of the prop can make a lot of difference in speed and RPM.

Iboats Boat and Motor Info

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor IMPORTANT
8. Manufacturer?s recommended WOT range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from prop, how much gas and how many people in boat for test data

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.

H

 

[MikDee]

Re: Prop performance Q...

Greetings,
I have a Mastercraft American Skier with a 13 x 13, three blade prop on it that gives me about 42 mph @ 4000-4100 RPM. I had purchased a 13 x 16, four blade prop and would like to know what the difference in preformance it will give me. Will I sacrifice top end speed if I switch?

Yes! You're not even spinning enough rpm with the 13" prop, it should be between 4200-4600 rpm, with that 16" 4 blade, you'll probably lose at least 500rpm, and be lugging your motor even worse!

 

[frustratedboater]

Re: Prop performance Q...

Thanks for the welcome. I have a 1985 American Skier with a Chevy 350, velvet drive 1 1/8" shaft and a 13 x 13 bronze prop. It does not sport a deep "V", it is 19.5' in length, I usually hold 15-20 gallons of fuel, 2 adults, 4 kids, WOT 43 MPH @ 4200 RPM (just me), WOT 39 MPH @ 4000 RPM (full payload, and has a plate coming off the transome, but no trim tabs.

I purchased the boat 'as is' and didn't come with any specifications... I have purchased a 13 x 16 four blade prop, but don't have a puller to install it. I'd like to know my options first. Thanks,

~FB~

 

[hwsiii]

Re: Prop performance Q...

Frustrated, I am sorry to tell you that Mik is 100% right, you don't stand a chance of being able to turn that prop any where near the RPM you are turning now. You need to actually use a smaller prop than the 13 x 13 you now have on it NOT larger. I don't have enough information to run any numbers for you but you would do much better with about a 13 x 11" pitch prop.


H

 

[frustratedboater]

Re: Prop performance Q...

Thanks for the bad news! I understand... Anyone want to buy a brass 13 x 16 prop??? What is the best place to purchase a 13 x 11 prop?

 

[countvlad]

Re: Prop performance Q...

Thanks for the bad news! I understand... Anyone want to buy a brass 13 x 16 prop??? What is the best place to purchase a 13 x 11 prop?

best place?? try the dealer its posible they might have an exchage program if you are not happy with the prop.... then compare the prices with the iboats props website http://boatpropellers.iboats.com/ .... good luck

 

[MikDee]

Re: Prop performance Q...

Thanks for the bad news! I understand... Anyone want to buy a brass 13 x 16 prop??? What is the best place to purchase a 13 x 11 prop?

You need to go over your motor real good, it sounds like somethings wrong, it should be turning 4200-4600rpm with the orig. prop. Replace the fuel filters, including the spin on, & the one in the carb, and give it a good tune up, if you haven't already

 

[countvlad]

Re: Prop performance Q...

Greetings,
I have a Mastercraft American Skier with a 13 x 13, three blade prop on it that gives me about 42 mph @ 4000-4100 RPM. I had purchased a 13 x 16, four blade prop and would like to know what the difference in preformance it will give me. Will I sacrifice top end speed if I switch?

if everything works fine and you are turning 4100 with that prop then you need to drop it down at least a pitch or two.....

the 4 blade is way too much for you... i wouldnt even bother installing it.. return it....

 

[frustratedboater]

Re: Prop performance Q...

I agree. With all the weight (family most of the time) I'd be pulling around, I guess I'd be looking for a shallower pitched blade. I'm looking for the 'all around' prop that will give me good top end as well. I thought, when I bought the 13 x 16, I'd give me that, and a great hole shot, but I guess it doesn't work that way.

I had my carb professionally rebuilt--had to have it acid dipped to clear some junk. There's a good speed shop by Dover International, here in DE, that tuned the carb when they put it back on the boat. The fuel filter is brand new... etc. I was cruzin' with the whole family Sunday when I posted the results to you guys. The boat is a bit more responsive when it is just me. I heard of Mastercrafts pulling 10 skiers, so I was hopeful of a blade that gives the same results!

~FB~

 

[countvlad]

Re: Prop performance Q...

I agree. With all the weight (family most of the time) I'd be pulling around, I guess I'd be looking for a shallower pitched blade. I'm looking for the 'all around' prop that will give me good top end as well. I thought, when I bought the 13 x 16, I'd give me that, and a great hole shot, but I guess it doesn't work that way.

I had my carb professionally rebuilt--had to have it acid dipped to clear some junk. There's a good speed shop by Dover International, here in DE, that tuned the carb when they put it back on the boat. The fuel filter is brand new... etc. I was cruzin' with the whole family Sunday when I posted the results to you guys. The boat is a bit more responsive when it is just me. I heard of Mastercrafts pulling 10 skiers, so I was hopeful of a blade that gives the same results!

~FB~

keep us updated once you get a diffrent prop

 

[MikDee]

Re: Prop performance Q...

What year is the boat? Is it electronic ignition, or breaker points? Maybe your advance is not working fully (sticking)? If it's a 351 Ford, or 350 Chevy, That boat should be doing 45mph easy with that prop!

 

[frustratedboater]

Re: Prop performance Q...

The year is 1985. It is a Chevy 350 rather than the origional 351 (I purchased it that way). It still has a Mallory breaker point setup (not duel points, but single). I had cleaned up the advance weights and seemed to be swinging out fine, but I should check them.

"That boat should be doing 45mph easy with that prop!" The 13 x 13, or the 13 x 16?

 

[MikDee]

Re: Prop performance Q...

The year is 1985. It is a Chevy 350 rather than the origional 351 (I purchased it that way). It still has a Mallory breaker point setup (not duel points, but single). I had cleaned up the advance weights and seemed to be swinging out fine, but I should check them.

Okay, make sure your points are set right, a dwell meter is best for this, but you can get them close enough with a feeler gauge. Once they are moved at all, you must reset your timing! It wouldn't hurt to check the timing at this time anyway.Also, make sure your flame arrestor is clean, and that your throttle, & 4bbl are opening all the way.

"That boat should be doing 45mph easy with that prop!" The 13 x 13, or the 13 x 16?

I meant with the 13"x13" prop, being a skiboat it has direct drive to the prop, (no reduction gearing) here's my formula for approx. speed - 4600rpm X 12" pitch, (pitch -1) = 55.2mph minus average 15% slip = 46.90mph net, Slip can be 10-20% avg.

 

[frustratedboater]

Re: Prop performance Q...

Thanks for the good advice on the engine tune and should go back and see what it doing. I don't have a dwell meter and should have one, but I believe I have the points set at .018, but I will recheck them. I will also see where the timing is after that. Should the timing be 8 degrees BTDC? I don't have a manual on the boat/engine that tells me.

 

[MikDee]

Re: Prop performance Q...

I don't have a service book for your engine for reference either, but the average settings for a 350 Chevy Mercruiser is .018 points gap and a timing setting of 8* advance.