How do you find the original Prop spec's?

[Lrider]

I have a 96 Johnson 88 SPL it has a COMPROP 4x13.5x15 P/N O4345

The prop is one of their first composites - so is about 10 years old, I would like to get an aluminum prop (heh as a spare?)

I really know nothing about how the prop effects the boat performance

 

[Silvertip]

Re: How do you find the original Prop spec's?

All you need to know is the best prop is one that allows the engine to run at or very near the upper end of the manufacturers recommended wide open throttle rpm band. Performance will be whatever that prop provides. If for example the rpm band for your engine is 5000 - 5500 and your engine only spins 4900 rpm with an average load at wide open throttle you need to decrease pitch to bring the rpm up. That does not mean the boat goes faster -- it means the engine revs faster because the prop takes less bite on the water so it must spin faster to maintain the same speed as before. In severe cases of over propping, decreasing pitch can actually increase speed as the engine gets "over the hump" so to speak and can get on its power band. Conversely, if the engine over revs (higher than 5500) then you increase pitch and that should increase speed.

 

[steelespike]

Re: How do you find the original Prop spec's?

If you read the stickies at the top of the page and the helps on the prop store page it may help you understand prop selection better.
If your going to get a prop this is the time to improve your selection.You should select a replacement based on the performance of your present prop. max rpm and speed.Wouldn't hurt to give us the details of your boat and your typical load and activities.We can help you make a selection.

 

[Lrider]

Re: How do you find the original Prop spec's?

Wouldn't hurt to give us the details of your boat and your typical load and activities.We can help you make a selection.

The boat is a 1995 Sailfish 176 CC, it is 17' 6" long weighs in at 1500# dry
Has a 65 Gallon tank (I don't see filling it up any time soon) I keep about 25 gallons in it.

It has a variable Deadrise - 14 to 15 degrees

The current prop is a comprop 13.5 dia., 4 blade 15 pitch model 04345. It was their first production model.

I like what it does, that may change when I take the whale fin off.

What I am looking for is the equivalent prop in aluminum or SS

 

[Silvertip]

Re: How do you find the original Prop spec's?

There is no "equivalent" so to speak when you change propeller designs as well as manufacturers. A 15P three blade aluminum prop from manufacturer "A" for example rarely performs the same as a 15P three blade aluminum prop from manufacturer "B". It is called "design" which includes more than just pitch and diameter. Rake, blade shape, cupping, finish, hub etc., all affect performance. One manufacturer will bias hole shot at the sacrifice of top end. Another may bias top end at the cost of hole shot. Others shoot for a compromise. An then there is the age old problem of some props perform better on one hull design than another. So a prop that has poor hole shot on one style of boat may have excellent hole shot on another. That is why larger HP engines don't even come with props from the manufacturer. They simply don't know what boat the motor will be installed on so it is the dealer that makes that selection.

 

[Lrider]

Re: How do you find the original Prop spec's?

Thanks for the information Silvertip, looks like I am going to buy another Comprop as a spare. I don't have the money to experiment with all of the designs.

You think prop dealers have loaners?

 

[ondarvr]

Re: How do you find the original Prop spec's?

You typically don't need a bunch of money to find the right prop. Most good dealers will let you exchange props until you find the one you need if they have them in stock, just don't damage it.

 

[steelespike]

Re: How do you find the original Prop spec's?

If you get us your max rpm and speed and your motors rated rpm we can help you make that selection.Your composte may be the perfect size but without those figures there is no way to know.Also keep in mind if the composite strikes something it is more likely to have a total failure.Aluminum is more likely to survive and is repairable.Its true that changing material and brand can introduce complications.
As suggested there are dealers that will let you try props till you find the right one.
Usually requires a deposit or a purchase with an exchaunge to find the perfect fit.
It does require a tach and gps or speedometer.tiny tach is about $40 and easy to install. One for your motor will fit any 4 cylinder 2 stroke without regard to stator poles.