Thread: 500 HP not enough?
05-28-2006, 05:39 AM #1
500 HP not enough?
With twin 250HP 4 Tec's you would think after all the mods it runs 66.8 at 7800 RPMs (Stock Impellers). New custom impellers from Skat. I went from 4 blades prop that were 10/21's to three blades that are 13/17's. Test day and the air temp was about 75 degrees and humid from the best run I had previously made at 65 temp no humidity. And the boat ran 67 MPH at 8250 to 8300. My question is I gained 400 to 500 RPMs and only gained .02 of a MPH. Does this seem right? I'm not sure what my next step should be. What do you think? Is that all she wrote? Is there no more speed left? I think it may have ran better with the 4 blades. What do you guy's think?
05-28-2006, 08:53 AM #2
your re-inventing the wheel...I think you are the first guy that I have ever heard of modifying thier boat.....
You probably have alot of prop testing to do physics are probably ALOT different with the boats than that of the ski...
What diameter are the props on the boats???
05-28-2006, 10:31 AM #3
Re-inventing the wheel? His motor pumps and the like are identical to whats run on RXP's
05-28-2006, 11:25 AM #4
yea same parts... but parts do NOTHING without proper tuning. he's re-inventing tuning that machine is what two2 is saying.
different hull, different weight, different water dynamics, different everything... no one has ANY IDEA how speed and RPMs are related on a jetboat and how sensitive it is to top performance...
there's alot of trail and error ahead of you despite how similar it is to a PWC
05-28-2006, 01:54 PM #5
I understand the inherent differences between the pwc's and jetboats I was just bein' a jacka$$...
Don't worry somefun...we'll get this figured out and then we'll be blasting by those damn jetboat hatin' prop spinnin' outboard meat spinners
05-29-2006, 07:19 AM #6
Yeah same pumps. I had it out yesterday and it ran great but I do think there is a lot more slip with the 3 blades.. I think the ideal set up for mine would be four blades 10/ 19. I my have Glen at Skat take a little out of the stock units or make some new 4 blades. It seems to handle better with the four blades. Have you guy's noticed that on your ski's?
05-29-2006, 12:54 PM #7
Well I haven't received my skat 3 blade yet somefun...so I took my stocker out and took the wrench to it I must have stuck it in that watcon impeller pitch gauge a 1000 times I decided to start with 12/19 and see where that takes me. I know most people just adjust the trailing edge but I figured I'd take a stab at the whole thing. I made sure to keep a a real smooth pitch transition (not wavy). I measured, remeasured, plotted, deciphered, scratched head and stayed up till 4am working on it
Looking at my stock impeller before any bends I couldn't believe how out of wack it was Only one blade measured the factory 10/21...the others were 11/19, 11/18, 12/20. I don't know how much the watcon angles relate to Seadoo's way of measuring but the blades were all different. I took measurements all along the length of the blades to determine if the pitch changes happened linear or if there was more pitch bend a certain intervals. Seems to be linear...Ultimately, making the blades all identical in pitch bend (leading edge > trailing edge) while maintaining outside diameter is the goal. This must be what they do when they blueprint them and weld on more material if it becomes a too small.
I'll keep you posted... my fingers are crossed that I didn't make the wife a new stainless steel egg beater lol! I'm going to pick up some calipers so I can measure the outside diameter, this is important as you don't want to put too much bend causing a gap between impeller and wear ring. Says it should have no more then 0.35mm (.014 in) clearance between wear ring and impeller.
I know yer sending yours to the experts but maybe some of this tinkering by this putz will yield some data that will be helpful to you.
05-29-2006, 07:13 PM #8
05-29-2006, 07:36 PM #9
somefun.... i had a thought yesterday while riding my dad's ski. it was boring and uneventful... i didn't realize how boring a stock 04 GTX SC was but anyway, i saw a Seadoo utopia jetboat, watched to see it take off bc they are actually fast boats those Utopias...
well i started thinking about you and your boat....
there's no trim or anything like that.... what if you added some seriously pitched pump wedges to both pumps on your boat. That would get that boat very much out of the water and i think you might see a pretty large gain POSSIBLY
has this thought crossed your mind about adding maybe twin 2.5 egree wedges to each pump... so u got 5 degrees on each engine. that boat will be real high outta the water and reduce the surface area.
jsut a thought....
05-29-2006, 10:01 PM #10
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