Too much prop slip 28 Heat
 

Running a 28P Bravo 1 Labbed by BBlades and still running 18% prop slip. Is this standard for the Heat and High HP?
800+hp
1 inch spacer
I can adjust my redline to 6500 but i dont want to do that. Right now it set at 5200 I will raise to 5600 this weekend.
Even after installing the labbed prop it wants to cavitate or blow out right after coming on plane.
Would i be better going to a 30p Bravo I.
Sometimes we get 74 mph sometimes we get 78. I haven't been able to detail the reasons yet. One variable i had was having two passengers on the OB. Both times i had bimini up.
Full fuel on all runs

What conditions do you get best speed with the Stepped hull Heat?

I would suggest taking the top down for sure

Also if it's a mcob put your snap cover over the OB to get the most speed

we found that we have spark plug gap too wide, its set at .060 not .035, air filter is being sucked in and collapsing, pro charger said we need to run just the screen or much bigger filter, tuner said change plug gap and run the coils as one may be bad.

i run a 5 blade 30p. 5600RPM, 90+MPH. closed bow, ISC600, i do get some cavitation coming on plane when the turbulence from the step is aligned with the prop. But it accelerators thru the cavitational period (20-30mph) and grabs.

What prop?

I recently switched props this summer and here are my findings:
2004 Nordic Heat open bow with a stock 496HO. Bravo X drive with 1" spacer. Was running a 24P labbed bravo 1 4 blade and it had 18% slip at WOT. 5000 RPMs (I had 2 labbed 24p bravo props and the results were the same)

Based on what Bob Teague said about the Nordic Heat and a Max 5 prop in his Teague talk propeller video, I got a Max 5 prop at 23 pitch and gained 3MPH on top at the same 5000 RPMs. Prop slip at 14% at WOT. Boat handles better is every aspect, doesn't blow out while coming on plane anymore. Very impressed. And my cruise speed increased even more, although I don't have an accurate measurement on how much exactly.

I'm going to stick with the max 5 props when I increase HP in the future.

That good news, I think some guy were using a hydromotive prop too? My 28 has about 14% slip, the 30P is 18+% which may be because of its condition.

The Hydromotive P5X 5 blade was a popular choice for some of the guys (especially with higher HP) that did a bunch of prop testing with the Heats. It's interesting the Max 5 does resemble the P5X in design, so it makes sense. There's a few other companies that are developing or recently released 5 blade propellers. BBlades, Hill Signature, Cutting Edge to name some. It seems like the accepted "Bravo 1 standard performance prop" may be heading in the five blade direction with these stepped hull high X dimension hulls.

Maximus 5 blade, 30P

I have a 2000 Obmc heat with a single 750 running an Imco SCX and a Maximus 5b @p28 slipping 18%... I see 81mph at 5500rpm. Used to run 85 with the XR.. my prop shaft is only 2” from
the bottom of the boat now with the Imco drive. Would I find that speed again with a 1-2” spacer. After 70mph it also walks/chimes more than it used too with the xr drive

what’s the XD on your boat?

Centerline of propshaft is roughly 1.5" above bottom of boat. This measurement was done using a level on the bottom of the boat to extend the front of the outdrive. Measurement taken with trim in neutral position parallel with bottom of boat. Neutral trim is my best performance also.

I may have misspoke. I don't believe i actually have cavitation coming onto plane. As i come up onto a plane and the boat is accelerating between 20 and 30 MPH, the prop is transitioning from having all 5 blades in the water to only the lower 1/2 of the blades biting the water. During this transition, there is some add'l slip that goes completely away by 30-35 MPH. I also raise the trim to neutral during the transition between 20 to 35 MPH. i don't believe i have any serious cavitation where a vapor filled cavity is created around the prop. No expert, only an assessment.

does your walk/chime at higher speeds. 75+?

Yes, it's a handful above 75-80. I do NOT have trim tabs and I run the Maximus 5 30p with the diffuser ring still on it (stock config). I've thought about taking off the diffuser ring to reduce transom lift. I would love to hear from other Heat owners that run in the 80's and see what they have done to create more stability.

You're thinking of adding the spacer to drop the prop shaft down so the centerline of the shaft is parallel with the bottom?

With our old engine we run to 87 mph Very easily. No chine, no issues at all. This is spinning a labbed 32p bravo 1 labbed by Merc racing. We have tabs never use them. I do have video of us along side a fountain that is chine walking like crazy. If you want to see the video I can post on you tube. Our heat is
https://cimg7.ibsrv.net/gimg/www.off...f5d072c90.jpeg
Heat on right chap on left, his hers boats
https://cimg9.ibsrv.net/gimg/www.off...5220c4bf0.jpeg
This is our gps track last year with me and my boys running the Colorado with friends. Later that afternoon we ran south again and met up with the fountain.

@Cerberus66
Thanks! Are you in PHX area? Maybe one day and you can show me how to run the Colorado. I just relocated from WA state. Currently boating in NORCAL Delta and Tahoe before towing south next fall.

We go to havasu. Almost every weekend during the warm season. We run from Parker to topock.

Here is our new motor. Installing it next week.
https://cimg7.ibsrv.net/gimg/www.off...c90a76a56.jpeg

the prop shaft on mine is 2” below the bottom of the boat now, but it was more like 4” with my XR before switching to an Imco SCX. I think lowering the drive into the water more would fix the walk/chiming. I talked to Brett from Bblades and am sending the p28 Maximus to be labbed. He says they can get my slip numbers down from 17.7% with the lab. then we should look at drive spacers to get it dialed in to 10ish% slip range which should have me in the mid 80s hopefully with less walking. I will be completely happy with a 85+ mph open bow heat.

what power do you have?

I don’t have a dyno but I gotta be 750-800
punched 502 to a 509. 8.5:1 comp, dart pro 1 heads
custom cam, 2.3l whipple @ 9 psi. Cmi headers, All aeromotive pumps and fuel coolers

The experimentation done years ago by fellow Nordic owners showed us that 4.5" below the keel on a stepped hull Heat was the sweet spot for the best speed and handling. A 1" spacer on my Bravo drive achieved the 4.5" for me on my 2004 Heat, and I noticed an improvement. I especially noticed a reduction in the cavitation coming onto plane (I was running a labbed Bravo One 4 blade at the time) I don't know that this information applies the same to an Imco drive.

the Imco is two inches shorter than the XR that came off the boat and sits a perfect 2 inches from the keel on my heat. The biggest spacer Imco makes is 2” and could get me to 4.
I’m going to see what labbing my maximus p28 does for my slip of 17.7% then consider a spacer. One step at a time