SteveDavid

Hi guys,
Tested the 5 blade Hydromotives on Sunday. In a word, they are AWESOME!! I was truly stunned with their all around performance. Getting on plane was effortless with about 1/2 the bowrise of the Bravos. Absolutely no cavitation getting on plane. Will stay on plane at 2200 RPM. They carried the boat at WOT like it was a hydrostream. Slip is down to 11% from over 23% with the Bravos. These were 15 1/2 X 32 with very large cup, and diffuser rings. My RPMs we're 100-200 less than with the Bravos yet over 5 MPH quicker.

These were loaner props from Ben Robertson at Fountain. I'm sold! Ordered 3 new ones, will be 15.5 diamter X 31 pitch with full cup, and diffuser rings.

I would never have believed the difference these props made had I not tried them. This goes back to not really knowing what something will do until you test it on your specific set up.

Take care,

Steve

Brad Perry

Steve,

Are you saying that your black thunder is now doing over 100mph with these new props?

I looked at hydromotive's description and preferred application of these props. Most all of their props are listed for boats that do not require much if any bow lift. Can you fill us in on you take of the bow lift or trim sensitivity of your boat with this prop?

Thanks.

[ 02-08-2002: Message edited by: Brad Perry ]

tomcat

Thanks for the info! My question is the same as Brad's. My boat is fastest with Hydromotive Quad IV, but they don't lift the bow enough, and guys who added the diffuser rings got more bowlift but lost the speed. That's exactly what happened when I put the Bravos on, but I just didn't like the feel of the boat with the Hydros. I don't remember, what is the position of the propshafts on your boat?

HavasuCat

Cobra Marty,

Good luck with the drive, I am in about the same ballpark with you as far as hp is concerned and my XR has been fine so far. Someday I want to pull my 510 and replace it with a 581 (1000 hp). I might have to re-gear again if I do.

SteveDavid

Brad and Tomcat,

The answer is yes and no. Yes in that it runs 101 on GPS but that's with the ECM rev limiters un set and turning almost 5700 RPM. So it's no for my everyday boating where we've set the ECM limiters at 5400.
The 5 blades haven't necessarily provided more bow lift, they've provided constant lift through out the planing attitude. Due to the nature of the Black Thunder hull design, angles of attack, rocker etc. these props have freed up the bow in equivalent measures to the rest of the boat giving a freer, less wetted ride.

I don't have the new 31's yet, but I'm suspecting the same ride qualities as the 32's we tested, just more RPM and with that maybe, and that's maybe 1-2 MPH.

The test's will be somewhat skewed as we've pulled those engines and are replacing with very similar powerplants, albeit another 30 HP per engine. That HP gain is via a different cam profile and Merlin heads as opposed to the GM performance heads that come std. on 500 EFI's.

As to the diffuser VS no diffuser, I believe each of us will experience a different result based on our hulls. Probably two Black Thunders of the similar weight would experience the same thing. However a Cat or a lighter Vee hull would experience something different. During one of the tests I ran diffusers on the outer drives and no diffuser on the center drive. All were the same pitch. The center drive ran about 150 RPM more than the outers, and still no cavitation. Then we ran with 1 engine off to test load and cavitation. At that time, the non diffuser prop tended to cavitate quite a bit getting on plane while the diffuser ring prop didn't cavitate at all.

Ran it again with all three engines and none of the props cavitated. Then ran with middle prop and a diffuser and the outers with no diffusers. Same results as above, no cavitaiton with all three running, the non diffuser props cavitated getting on plane while the prop with a diffuser ring didn't cavitate on two engines.

Whether this is strictly a function of the props (diffuser V no diffuser) or more a function of the Bravo hydrodynamics hasn't been determined. I'd have to run all the same tests using different lower units such as IMCOs and then the Bravos to ascertain that answer. However, the budget kind of got hammered with the new engines so I think I'm going to just enjoy the new engines and props for a while and not worry about what's still possible. At least for a while

Take care,

Steve

Garry

Steve I have spoken with Hydromotive and talked to them about the 5 blade. They seem to think it will help in the plaining dept. The problem is they only have the 31 available and we are hitting the rev limiter now with a stock bravo 32.
Do you think the 31 will be to small?
Also shot me a private e mail if you like on what you are paying. When I made the order my jaw dropped at the price.

[ 02-10-2002: Message edited by: Garry ]

BigGrizzly

I know Hydromotive is working on bigger props .

Randy

SteveDavid

Garry,

Big Grizzly is on the mark, they will have larger pitch props in the near future. The one I tested were Benny's and he was assisting them.

I think you'll find the 31 will pull more akin to a 33 Bravo and might keep you within redline. The diameter is 1/4 inch larger, and the 5th. blade will load your engine more than the bravo is.

Tell you what, when I get my new ones, how about I loan you one and you see what it does. If it works well, the price might be more palatable. I'm supposed to receive them in the next 10 to 14 days. I won't have my boat back together for probably 3 weeks, so that will give us a window of one week to get it to you, test it and get it back when my boat is ready.

Same deal as last time, you absorb the shipping and the prop itself is free to try?

Steve

US1 Fountain

iTrader: (1)

My problem is that anything under 30 and the boat falls off plane. Either that or tabs all the way down, nose pointed sky high and boat plowing thru the water parting the seas. This can't be good for the Bravo. Same with both my 24 & 27" Hydro Q-IV's. So would something like a Bravo 4 blade help out with this because of the full round ear blades?
And whats your guys take on switching to a RH prop after using LH since new in '94? Have had the mention of shafts taking on a twisted set, thus weaking them when reversing rotation. I would like to switch rotations if I buy another prop placing the force in the lower housing vs. the upper cap.
Thanks,
Jerry

cobra marty

Steve, Sorry to hear about your engine troubles. Did you get the Merlin crate 509 cid 540 HP motors? What a shame you could have sold the 500efi's and started aftermarket from the start. Your testing and running commentary has been terrific.