Prop Question

[Bossman]

I need a new prop. My main one is too thin to fix...So A few questions I guess..first My application:
16ft Smokercraft with a 50hp 2 stroke Merc

I have been running 3 blade props but I may go a 4 blade just for better handling in rough water(So I have been told) I have heard 4 blade will reduce top speed..My top speed is only about 30mph(lightly loaded)..Will going 4 blade affect it a lot?

I was told it is a 10.5 x 13..I am shopping online for one and I see some that are listed as 10.5 x 11/ 13 spline..Would that work for my application? See link below on one I found..I just want to make sure I get the correct one as to not do damage to the engine...Thanks!!

https://www.amazon.com/dp/B01J8DNT2A/?tag=nodakangler10-20

 

[Allen]

At one point I had a 16 ft Smokercraft with a 75 horse Mariner on it. It did something in the upper 30s, but was a chine-walking SOB, especially at the tailrace when running up into the chutes. I ran a composite 4-blade on it until the river eventually claimed it, I don't think it knocked anything off of the top-end speed, but it did give the prop a really good hold on the water when turning while at full trim for speed. Three blade props tended to blow out a little more, granted...this is when I was a lot poorer and I was too cheap to buy SS props. Of course, SS props don't flex much at all compared to aluminum, and surely not nearly as much as a composite.

All in all, I liked the composite 4-blade. Even though they are inexpensive, they aren't very durable if you find yourself in shallow water often.

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note: the composite prop is extra insurance against damaging the lower unit in case of rock hits, etc. Just make sure you keep a spare prop in the boat with you.

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p.s. Do you know your RPMs? Going down a couple of inches in pitch will boost the RPMS and probably slow your boat overall.

I thought my composite prop was an easy spinner compared to either aluminum or SS. I'd probably want to try the same pitch you already have (13") before going down a full two inches. Again, at the price, I'd suggest buying two but would probably want to start with the 13" if my RPMs were already in the zone.

 

[Colonel Angus]

Had a 90 merc with a 17p 3blade allum, and went to a 17p SS 4 blade. lost about 3mph top end and dropped the rpm about 200 at full throttle. The hole shot and handling in rough water and pulling skiers and tubers was well worth it though. It was like putting new tires on the 4x4. You can check out the Mercury Marine website. They have a prop selector page you can put info into that can be helpful.

 

[Bossman]

Do those numbers seem right to you guys? The shop said 10.5 x13 they didn't have that "11" in there like I am seeing on-line when I search..I'm thinking the 11 is another measurement and I just need to make sure the 10.5 and the 13 spine is right?...Just want to make 100% sure...Thanks for the replies so far..

 

[Allen]

In prop numbers, it's diameter x pitch. That last little bit of info on spline count is unnecessary unless there's something I am unaware of with older Merc motors having a couple of different prop shaft options.

http://comprop.com/#1465318457172-4f615e2e-4aec

I see on the above link that at Comprop (I'm sure there are other manufacturers of composite props), a 50 HP Mercury prop from them has only two options for dia/pitch and just one option on shaft splining.

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e.g. the spline count tells you what props are made to fit your motor.

 

[Bossman]

Thanks for the info. Allen..But according to your link and you stating to not take into account the spline number and using the #'s the shop gave me of 10.5 x 13 the prop I need isn't available?

 

[Wildyote]

I need a new prop. My main one is too thin to fix...So A few questions I guess..first My application:
16ft Smokercraft with a 50hp 2 stroke Merc

I have been running 3 blade props but I may go a 4 blade just for better handling in rough water(So I have been told) I have heard 4 blade will reduce top speed..My top speed is only about 30mph(lightly loaded)..Will going 4 blade affect it a lot?

I was told it is a 10.5 x 13..I am shopping online for one and I see some that are listed as 10.5 x 11/ 13 spline..Would that work for my application? See link below on one I found..I just want to make sure I get the correct one as to not do damage to the engine...Thanks!!

https://www.amazon.com/dp/B01J8DNT2A/?tag=nodakangler10-20

I have 2 friends that have owned the same boat you got although they were 17 footers. The prop is only going to possibly fix part of the problems. I would imagine your boat has some porpoising issues in rough water. The 4 blade can give you better grip and probably not affect your speed much. I have a 18.5 glass lund and had some porpoising issues in rough water or heavy load of people. The dealer I purchased the boat from fixed the problem which lund should have done from the start. The mechanic dropped the motor a hole and I went to a four blade. I have no more issues other than I would get on plane a touch faster.

I would install an edge plate or hydrofoil it will help you get on plane and keep your bow down while on plane. Try yo moves as much weight as you can up front.

Now the harsh truth....Your model boat is a nice boat to fish many waters in calm seas but when you go to Devils Lake and main lake Oahe or Sakakawea you will get a beating when the wind picks up. The problem is it has a short light hull. Many of the Crestliner, Smokercraftm, and Sylvan are notorious for this, You can have a boat mechanic add a hook on the back of your boat and bottom of your transom.

The bright side, you just have to pick your days but most importantly lakes you fish and locations on bigger lakes.

 

[eyexer]

when you go from aluminum to stainless you usually have to drop in pitch

 

[Allen]

Thanks for the info. Allen..But according to your link and you stating to not take into account the spline number and using the #'s the shop gave me of 10.5 x 13 the prop I need isn't available?

Right, ComProp makes a 10x13, not a 10.5" diameter. This is actually pretty common where a given manufacturer makes a series of props for a boat motor and they make the higher pitches in a slightly smaller diameter. I "think" it is to help them spin easier compared to a similar diameter prop that is a full 2 inches more in pitch. While a half inch difference is quite a bit in diameter, there is no reason why you can't use a 10" diameter prop if you were set on the 13" pitch.

In other words, I don't know why a shop would tell you that you need to use a specific diameter prop.

 

[Bossman]

Right, ComProp makes a 10x13, not a 10.5" diameter. This is actually pretty common where a given manufacturer makes a series of props for a boat motor and they make the higher pitches in a slightly smaller diameter. I "think" it is to help them spin easier compared to a similar diameter prop that is a full 2 inches more in pitch. While a half inch difference is quite a bit in diameter, there is no reason why you can't use a 10" diameter prop if you were set on the 13" pitch.

In other words, I don't know why a shop would tell you that you need to use a specific diameter prop.

That makes sense..Thanks for the feedback, greatly appreciated!