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-   -   HP vs pitch (https://www.offshoreonly.com/forums/prop-talk/324318-hp-vs-pitch.html)

arttu 06-22-2015 02:54 PM

Blower installed and tested :) Yeah there is a "little" bit more power and torque :)

I tried 27p solas L3 and had huge problems lifting boat to planing, slipped horrible at the start. There was enough power to spin it when finally got boat planing but acceleration was impossible so ditching that prop.

With current mirage 23p it`s like drag boat and engine revs about 6000rpm top speed of 69mph. I actually like the acceleration but would like to have little more cruising speed and maybe top end speed, not spin the engine so damn fast.
I`m thinking to go 25p mirage+. What do you guys think would it give more cruising & top speed? It is more cupped than normal mirage, so I´m wondering will it be any faster or should I stick with my 23p?? Or try something else?

BBCLiberator 06-22-2015 04:10 PM


Originally Posted by arttu (Post 4320978)
Blower installed and tested :) Yeah there is a "little" bit more power and torque :)

I tried 27p solas L3 and had huge problems lifting boat to planing, slipped horrible at the start. There was enough power to spin it when finally got boat planing but acceleration was impossible so ditching that prop.

With current mirage 23p it`s like drag boat and engine revs about 6000rpm top speed of 69mph. I actually like the acceleration but would like to have little more cruising speed and maybe top end speed, not spin the engine so damn fast.
I`m thinking to go 25p mirage+. What do you guys think would it give more cruising & top speed? It is more cupped than normal mirage, so I´m wondering will it be any faster or should I stick with my 23p?? Or try something else?


You didn't say you had anything done to the internals of the motor, correct? If not, 6000rpm is asking for some fireworks. I would at least bump it up 2" to a 25 and try that. That will still only bring it down 500rpm or so…which is still to high for a 454 mag. I wouldn't want that engine over 5250rpm….which honestly is pushing it.

Good Luck!

arttu 06-23-2015 10:37 AM

^^exactly... If spinning same engine rpm, will mirage+ 25p be faster than normal mirage 23p??

himrod67 06-23-2015 11:47 AM

Yes

kidturbo 06-23-2015 12:39 PM


Originally Posted by arttu (Post 4321418)
^^exactly... If spinning same engine rpm, will mirage+ 25p be faster than normal mirage 23p??

Now is where using that prop calculator comes back into play to compare speed vs RPM again. You know it will spin 6000, so I'd jump up 2 or 3 in pitch and possibly find one in a 4 blade to try. Personal preference, but I like the hooked up feel of more blades even if it cost me a couple mph.

BBCLiberator 06-23-2015 03:35 PM

Sounds like we shoul explain pitch. Think pitch as inches. Every time the prop turns one full revolution, it will move that amount in inches if it were traveling through something solid. We know this isn't true completely and that is why you have some "slip". The higher the pitch the more it moves your boat per revolution, and the faster you go at the same engine RPM.

arttu 06-23-2015 04:22 PM


Originally Posted by BBCLiberator (Post 4321604)
Sounds like we shoul explain pitch. Think pitch as inches. Every time the prop turns one full revolution, it will move that amount in inches if it were traveling through something solid. We know this isn't true completely and that is why you have some "slip". The higher the pitch the more it moves your boat per revolution, and the faster you go at the same engine RPM.

Don`t worry I´m not that dumb as I look :) :) I Ment that there`s a difference in cupping between mirage and mirage+ props if understood correctly, so was wondering if this cupping reduce speed? Anyhow I ordered just cheap mirage+ 25p and hope that my rubex hub will fit in it. Prop had a square hub hole in pic... Let`s see how it works!

bbladesprops 06-24-2015 04:19 PM


Originally Posted by arttu (Post 4321626)
Don`t worry I´m not that dumb as I look :) :) I Ment that there`s a difference in cupping between mirage and mirage+ props if understood correctly, so was wondering if this cupping reduce speed? Anyhow I ordered just cheap mirage+ 25p and hope that my rubex hub will fit in it. Prop had a square hub hole in pic... Let`s see how it works!

The old Mirage was thinner with less cup. It was faster on efficient hulls.
The Mirage + has more cup and can be faster on less efficient hulls.

Brett

arttu 07-11-2015 07:41 AM

Hello! Now I have tried 25p mirage (non-plus).. It was ok but "blows out" just after planning. Need to reduce gas, it gets grip and then we go :) Top end was 72 mph @ 5500 rpm. So seems that my limit with 3-blades ends at 23p...

Now I think I´ll start testing 4-blades. I think I can bump pitch to 26. I found two props in Sweden. Bravo 1 26p and Turbo 2+2 26p. Bravo 1 is dia 15.25 and Turbo 2+2 dia says 14.25..

I´m wondering how much will lose "agression" of engine if bumping dia from present 14.5 to 15.25??? Or if reducing to 14.25 is there risk of blow out and slipping again? What do you think?

bbladesprops 07-13-2015 12:29 PM

The Bravo 1 is only 15" diameter. The marketing of the propeller suggests 15.25". The only 15.25" Bravo 1's are the 34 and 36.

Try them and see. Testing is the official answer to how they perform. Load the boat like you would in a normal boating day.

Brett


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