Bigger, smaller, or stay the same

[vstol]

I have decided to go to Stainless props on my Volvo 290DP lower unit it is a 1992 with a 431A in front. 20 foot open bow boat.

I have chewed up 3 sets now in 3 years with normal use (shallow water and obstacles like crab pots).

Should I stay with the same size as the aluminum (B7) or go down to a 6. I have heard that since there will not be any flex to go down a size, I have heard stay with the size that came on the boat, I have thought of going up a size?

Also there seems to be 2 kinds of stainless props for my boat, one a diesel and one gas, mine is gas but I don?t know the difference between the 2 props, one is a C7 one is a F7, which one do I use?

 

[Don S]

Re: Bigger, smaller, or stay the same

Moving to prop forum

 

[steelespike]

Re: Bigger, smaller, or stay the same

While there may be someone here with info specific to the volvo numbers.
We can also help you if we know the actual prop size and present max rpm and speed.Even with the Volvo numbers it is difficult to make an decision without the present max rpm and speed.

 

[vstol]

Re: Bigger, smaller, or stay the same

With the b7 (which are aluminum ones I have, I am able to get to the WOT of 4600 RPM, I have had B6 and seem to be a little under propped, could have over sped the engine if I opened it all the way up.

I was wondering more along the lines if i should stay with the size "X7" (the X being not sure i need C7 or F7 for stainless) or go down a size, i have heard with the weight of stainless and that they dont flex at high speeds that some people do go down a size. (High speeds on my boat is only about 45 on salt water.) What is the general consensus on that?

 

[BGutah]

Re: Bigger, smaller, or stay the same

That rubbish about prop flex comes from the guys trying to sell the stainless prop...if you really want stainless and are happy with the way your boat performs ...keep the same pitch...just be aware that all that force will now tranfer into your lower unit when you hit a shallow water obstacle...the prop wont break so something else has to give... although they look way on the boat

 

[rndn]

Re: Bigger, smaller, or stay the same

If you go through props that quickly stick with aluminum. As stated above the SS props tranfer much more energy(damage) to the drive system than aluminum. They are also cheaper to replace and/or fix than SS.

 

[twag4]

Re: Bigger, smaller, or stay the same

That rubbish about prop flex comes from the guys trying to sell the stainless prop...if you really want stainless and are happy with the way your boat performs ...keep the same pitch...just be aware that all that force will now tranfer into your lower unit when you hit a shallow water obstacle...the prop wont break so something else has to give... although they look way on the boat

I saw a demo at a boat show of several aluminum and stainless prop in a big glass tank. Aluminum props flex. It is a fact. Respectfully.