Propeller Advice

[andrewsailor]

Hi Everyone,I have an Allumacraft 165cs with a Yamaha 75 4 stroke motor and currently run a 13 x 19 prop,anyone know what the difference would be if I went to a 13 1/4 x 17 prop.The boat currently does 37 miles an hour and runs at 5500 rpm,would like to run a little faster. Does a larger daimeter and less pitch change anything?
Thanks

 

[hwsiii]

Re: Propeller Advice

Andrew, theoretically it will make the boat go slower, but that is not always true because the right blade geometry can make it go faster.
We will try to help you as much as we can, but there is certain information that is needed in order to help you. The following form has all of the information that is needed to help you with your problems 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 planning hull boat that needs this information, and anyone else who is 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
8. Manufacturer?s recommended WOT range
9. Antiventilation Plate height above keel of boat if it is an outboard in inches
10. Make, model, diameter, pitch and whether SS or aluminum prop
11. WOT RPM and speed from each prop

H

 

[andrewsailor]

Re: Propeller Advice

Alumacraft classic 165cs 2007
16'5 x 80"
2 people,18 gallons
Fishing
Deep Vee not sure of the rise
Yamaha F75 4 Stroke 2009
75 hp
5000-6000
Not sure about the plate as the boat is at the lake
Yamaha propeller,13 x 19 Alluminium
Hope this answers all the info you need,much appreciated looking forward to your answer
Andrew

 

[andrewsailor]

Re: Propeller Advice

Hi there H,The gear ratio is2.31
Thanks Andrew

 

[hwsiii]

Re: Propeller Advice

Andrew, by changing to a 17" pitch in the same model of propeller you would gain about 420 RPM and you should not lose any speed. The larger diameter may even help with your prop slip, which is at 14% right now.

Prop Change

Prop Slip

H

 

[andrewsailor]

Re: Propeller Advice

Hi there H,thanks for the info,very informative,I can get a 13 1/2 x 19 which with the larger daimeter should reduce slippage,give me a couple of extra mph without increasing engine rpm,hopefully
Thanks Again,Andrew

 

[hwsiii]

Re: Propeller Advice

Andrew, if you are talking about a SS prop it will definitely depend on blade geometry.

H

 

[andrewsailor]

Re: Propeller Advice

Hi H,it would be Aluminium

 

[Silvertip]

Re: Propeller Advice

That 1/4 inch in diameter will likely be unnoticeable. Prop diameter is a function of propeller design. Prop design includes blade shape, rake, pitch, material, and the actual diameter is set so the prop can be used on a specific range of engines. I suggest you forget a new prop and make sure the setup you have is optimized. Then break out your wallet and experiment with props. Some prop shops have a try before you buy program. You will quickly learn that a 13-1/4 x 19 prop from manufacturer "A" does not perform the same at a prop from manufacturer "B". They will be close but one will generally perform better heavily loaded, or perhaps hole shot will be better. The other may provide higher top speed with less hole shot. There is no free lunch when it comes to props.

 

[andrewsailor]

Re: Propeller Advice

Hi Silvertip,thanks for the info,there really is alot about props I didn't know.