Which prop should I choose?

[droo88]

Hi, I am unsure which prop I should choose:

I have a 15 foot fletcher with a 40hp Mercury 2 stroke 4 cylinder engine. Boat currently has a 10 1/8 x 15 blackmax prop and with 2 people onboard it rises on plane after about 6-7 seconds with WOT reaching a top speed of 30 mph at 5200 rpm.

When I have a full boat, with 4 people on board, the boat really struggles to get up on plane, taking up to 20 secs. Top speed is reduced to 24-25. I did not have a working tach then but I judge the rpms to be approx 4600-4700.

I am now looking at the Amita 3 prop (11.1 x 13) and the hustler 10.5x13.

What is the advantage of the bigger diameter of the solas prop? I am unsure if the rpm increase caused by the reduction in pitch would be offset by the increase in diameter.. the guy at the shop suggested that I take the amita 11.4 x 12 but I think that much reduction in pitch would end up killing my top speed.

What do you guys recommend? Amita 11.1x13 vs 11.4x12 vs hustler 10.5x13 ?

Thanks for your help!

 

[steelespike]

Re: Which prop should I choose?

What is the model,style,material/weight of the Fletcher.Year and model of the Merc.
A 15" pitch is only one step down from the highest pitch.More to come.

 

[steelespike]

Re: Which prop should I choose?

What is the model,style,material/weight of the Fletcher.Year and model of the Merc. Do you know the gear ratio?
A 15" pitch is only one step down from the highest pitch.More to come.
Theoretically a 13" prop should act like a 13" prop but what amounts to a 1" diameter difference
could affect the rpm. reducing the the rpm change slightly.100 or so.
The Solas Amita has a good reputation for predictable performance.
The Hustler is said to produces numbers close to ss performance, possibly with slightly less predictable resulted.
Sorry I can't be more specific.I think if you check the various Solas prop sizes that they tend to run bigger diameters.
You'll also note on any prop that usually as pitch goes down diameter goes up.

 

[droo88]

Re: Which prop should I choose?

The boat is a fletcher arrowflash, weight I think is about 200-250kg. Motor is a late 80's 40hp 2T 4-cylinder without oil injection. Gear ratio is 2:1.

I have attached a picture of the boat

I think a drop in pitch from the current 10 1/8x 15 to 11.4x 12 would be too drastic, do you agree? The larger diameter prop should slip less theoretically but I would still lose a lot of speed?

 

[droo88]

Re: Which prop should I choose?

The boat is a fletcher arrowflash, weight I think is about 200-250kg. Motor is a late 80's 40hp 2T 4-cylinder without oil injection. Gear ratio is 2:1.

I have attached a picture of the boat View attachment 207163

I think a drop in pitch from the current 10 1/8x 15 to 11.4x 12 would be too drastic, do you agree? The larger diameter prop should slip less theoretically but I would still lose a lot of speed?

 

[SkiDad]

Re: Which prop should I choose?

if it were me I'd try the 10.5x13 - makes more sense from what you currently have.

 

[steelespike]

Re: Which prop should I choose?

A 13 does seem like a reasonable approach.

 

[MARV1]

Re: Which prop should I choose?

11.1x13 is what I'd buy...

 

[droo88]

Re: Which prop should I choose?

Ordered the hustler 10.5x13 + hub kit off ebay..

Will let you know how it goes!

Thanks!