Do I need to go up in pitch with a cleaver ?

[QBhoy]

Hi
If going from a stainless laser 2 13&1/4x19"P to a 14x21"p stainless through Hub cleaver, should I expect the normal ruling on rpm change (around 400 rpm) or does the normal rule of thumb not apply with a cleaver ?
Thanks

 

[alldodge]

IMO you will see the 400 reduction if not a little more due to increase in diameter

 

[QBhoy]

Alldodge....
Was 100% thinking the same until I read an article about someone suggesting that to achieve similar RPM to a round blade prop, you would need to go up an inch or 2. I'm not sure if that's just one guys opinion or fact....that's the problem.
If the normal rules apply, I really don't want that because I didn't like a 13&1/4x21"p laser 2 when I tried it. Ran a bit faster but not as sweet.
If this cleaver was going to be the equivalent of a 19" or even better a 20" I'd be happy, but I can't afford for it to be worse than a 21" laser 2, given the larger diameter. Mmm

 

[alldodge]

Again just my opinion, the cleaver is designed to run on the surface, and most high performance boats have half the prop out of the water. The higher rake also gives you more lift. To use all the lift it can provide you need a boat which can use it. My thought is you don't so the prop will fully covered. Also keep in mind that increasing stern lift may cause some other issues to show up like proposing

 

[QBhoy]

No Title

Thanks Alldodge. Yeah it's a bit of an unknown really. Although she runs high up on the pad with the laser 2 doing a bit on surfacing every now and then. I'll maybe give it a go, it's cheap enough.

 

[Faztbullet]

Find you a Alpha SS upper drive (3" shorter than stock) and then run the cleaver...good for at least 8-10mph

 

[QBhoy]

Would love to find one of these...rare or like hens teeth in the UK, I'd imagine.