Pitch For Prop

[adzzy]

Hi

i was wondering what would happen to my 70hp yamaha if i changed the prop pitch from a 17 to a 19 would i get more speed at top end with less lift or vice versa

my old one has had it chips all over no paint left and one bent blade should i fork out the extra cash for stainless

Adzzy

[chrisg]

Hi

i was wondering what would happen to my 70hp yamaha if i changed the prop pitch from a 17 to a 19 would i get more speed at top end with less lift or vice versa

my old one has had it chips all over no paint left and one bent blade should i fork out the extra cash for stainless

Adzzy

You'll get more top end but lose on your hole shot. The deeper the V of your hull the more noticable that will be. If your prone to hitting things don't go the SS. They don't give and more shock is transferred to you gearbox.

Cheers

C.

Edited January 30, 2009 by chrisg

[WANNAFISH]

If the 17 pitch is working properly on the maximum rev limit I wouldnt change it. But if your motor is currently over revving change it. In theory 1 size up is 200rpm lost so 2 sizes up is approx. 400rpm.

I would go stainless if your sure your not gonna hit anything or else instead of the prop breaking your gonna need a gearbox which cost over a grand for a reco one.

[a boat]

Hi Adzzy, as mentioned if you can turn the 19 inch and still see about 5500RPM at WOT with your normal load than you will get more top speed and a lower cruising RPM, but the sacrifice will be acceration. What RPM was/is the 17 inch doing at WOT and that will determine if you can swing a 19 inch and not lug the engine which will shorten its life. I do not think your engine with have the torque to turn the 19 inch, your engine is only a 849cc engine and is not the most powerful 70HP/75HP on the market.

Cheers,

Huey.

[adzzy]

Hi Adzzy, as mentioned if you can turn the 19 inch and still see about 5500RPM at WOT with your normal load than you will get more top speed and a lower cruising RPM, but the sacrifice will be acceration. What RPM was/is the 17 inch doing at WOT and that will determine if you can swing a 19 inch and not lug the engine which will shorten its life. I do not think your engine with have the torque to turn the 19 inch, your engine is only a 849cc engine and is not the most powerful 70HP/75HP on the market.

Cheers,

Huey.

Hey Huey

what i want try and achieve is to get the nose down quicker at take off it is ok with two people on board but with 4 it is terrible if i go to a 15 pitch will this help?

i dont mind sacrificing top end speed as it is quick enough

im going to try a hydrofoil today should i get a cheapie or top end one?

At WOT it is about 5200 with two people and normal gear

Adzzy

[BFB]

A lower pitch prop will get the boat on the plane quicker as it gives a quicker acceleeration.

I used to use a lower pitch prop when pulling water skiers as top end wasn't a problem but I needed more punch out of the water.

[a boat]

Hey Huey

what i want try and achieve is to get the nose down quicker at take off it is ok with two people on board but with 4 it is terrible if i go to a 15 pitch will this help?

i dont mind sacrificing top end speed as it is quick enough

im going to try a hydrofoil today should i get a cheapie or top end one?

At WOT it is about 5200 with two people and normal gear

Adzzy

Hi Adzzy, going to a 15 inch prop will help with acceration when compared to the 17 inch you are running. It will plane the boat quicker and therefore the bow will not be pointing to the air as much. I you are only seeing 5200 with two people you are a bit over propped already and the 15 inch will be a much more suitabl prop and you could not run a 19 inch.

Cheers,

Huey.