Prop help for a 38 zr
 

I have a 38 zr with staggered 525's currently running 34 pitch 5 blade labbed props. Was out this weekend and was hitting the rev limits at about 80 mph. I know the boat has more than that. Any suggestions?

Are you sure they are 34 pitch 5 blades?

I have 34 pitch 5 blades on twin 700hp motors and pulling 115mph on my 38 ZRC.

They are 100% 34 pitch 5 blades.

ZR's with 525's usually run 30-31 pitch 5 blades, are they herings?

something dont sound right

They are not herings. My mechanic tells me i haven't found the boats sweet spot yet. I think he's just full of sh*t.

what rpm are you bumping the limiters? with 34s you should not be close to that... how are you trimming the boat? is this boat new to you?

It sounds to me like you are way over propped and are over trimming it to get the RPM up. The trim on a ZR should be at 2 to 3 max. anything over and you are over trimming it. I would bet dollars to donuts those are the wrong props for the boat.

Maybe he's running 1.65 gears.

I assume 525's came with XR drives, and they don't come in 1.65's that I know of. I think the lowest and standard is 1.5

My opinion is to do the math (i.e., get your ratio and figure out where you think you should be) then try some props.

Like Tom said the step bottom boats don't like trim like flat bottom boats do. I was on my limiters because my props were too small but now I'm doing well with bigger wheels but still pretty well neutral on the trim.

With big cruising wheels I can get to nearly the same speed by trimming out. So the prior owner might have put bigger ones on to max out cruising speed.

Herings were the faster prop on the ZR. Who's your mechanic? Mikey? Like everyones said you should not be able to swing the 34's to the limiters. A 4 blade maybe but not a Maximus.

Spoke to the guys at Donzi and they told me i was definetly running the wrong props. Just picked up a new set of 32 pitch 4 blade bravo props. Thanks for the input guys.

Did Donzi suggest those props? I dont believe a ZR ever really left the factory with 4 blades.

They have a lot of test data on hand and may have suggested the bravos as a reasonably priced alternative to the Herrings or the Maximus. Probably be a PITA to get up on plane though.

I spoke to Craig from Donzi and he told me that's the props i needed. Tried them out and so far a huge improvement. Pops on plane like nothing with full fuel and full load of people...

Still trying to find the sweet spot with trim and everything but gradually getting better.

On limiters with 34p 5 blades and the cure is 32p 4 blades?

Hmm makes no sense

38z,
I see you're from New Britain, do you ever make it down to LIS, there are a lot of OSO guys that launch out of the Old Saybrook area. Check out the NE section if you're interested in meeting up as guys are always posting where and what they are doing...

Scot

BTW, nice 38, we'd love to see it on the Sound!!! :cool:

38Z,
how are the new props running for you? What kind of top end are you seeing on MPH and RPMs? Need to do some tweaking on mine and nice to get some info before I go plunking down a bunch of money!
Thanks!

Trying 34p 4 blades this weekend trying to get a lil more out of the boat.

dreamer: Maybe you should become a boat builder???

SS930: I only run on the sound. Out every weekend the suns out which hasn't been much this year.

nick whats it running now for speeds and what kind of load you have on it????? Ask other Donzi guys but Id say the boat is really a 86-88mph boat on the average weekend with people, coolers, etc......If your already there then stop wasting your time with props.

i'm not there that's the problem.

Looking forward to seeing you out there then. :)

I'm no expert on 38 ZR's, but I'd guess the numbers you listed are probably on the high side and are probably close to the numbers one would see under light load and prime conditions. With people, coolers, fuel, etc, I'd guess routine everyday numbers would be closer to 82-84... but again that's just a guess.

I used to be able to run 88 with 3 people and 3/4 fuel in the summer any day, once hit 90.2 by myself with a lite load, with labbed 34p Maximus. Unfortunately cracked both props, sent one of them to a prop guy to replace with 2 identical props and they couldn't replicate them, in fact I lost like 12 mph and 650 rpm. I have been chasing the speed again, I have a feeling even though the originals said 34p(according to the serial number) that they had been cut down or something, because my new 34p Maximus are horrible. Hopefully the new ones can be bent to a 33p, cut down, or something to get the speed back. As I understand it every "recipe" for labbing a prop brings different results and that is why they couldn't replicate mine, but it sucks having a Formula run even with me, LOL!

Scott, those were very stout numbers... obviously well worked props, as you've obviously found to be the case. Based on your numbers, maybe Adam's numbers are more realistic than I would have thought with a decent set of props.

Adam's numbers are spot on with the right set-up and sweet spots for trim and tabs. My cousins 38 topgun runs 83 under the same power, passenger load, unstaggared, plus an extra couple thousand pounds of boat. I'll get there its just going to take some trial, error and patience.

Wow

updates?

Dunno if he found the right props yet but he threw a blade sat on the way long island.....we were heading there and he was idling back. Always something.....

34 pitch 4 blades were the right set up until i snapped a blade couple weeks ago which led to me grenading that same drive this weekend.

But on a up note i'm running in the mid to upper 80's now.

Ouch! XR's?

Glad to hear you got the boat moving like it should! :cool:

Yea XR's.

Thanks.

Do you know what exactly failed in the drive?

The upper blew apart. I guess it looked like a tooth broke free and tore everything apart up there...

That's the usual, probably not related to the prop though. If the other drive has the same hours on it, you might really want to think hard about tearing it apart too and replacing the upper gear. The gear is expensive (~$1500?), but it's a lot cheaper to catch it before it goes than to have to replace the entire upper. ;)

GL!

BTW, you might want to look into this if you're planning on keeping the boat or really running it...

http://www.offshoreonly.com/forums/g...-question.html

you need to cut out the caged roller bearing that comes with the gear set and replace it with a larger roller bearing(torington). use the same snap ring to hold the bearing in. doing this will take the rock out of the upper gear set. That is coming from a guy that blew a lot of uppers because of mercs screwed up design from the factory.

friend of mine just bought a new 38zr with 525's & it came with 34 maximus wheels. we ran it yesterday full of fuel & all it would run was 82 but rpm was 5000 with the trim set on 3. way high slip numbers for 5 blades. I don't think his boat would get up with 4 blades. any thoughts?

it'll bite harder with 4 blades and run the same speed but a little lower in the rpms. About 4800 to be exact. You'll be able to hang the drives out a little bit more also if you wanted to. The boat won't do more than 82-84 with a full load. You won't see the mid to upper 80's till half tanks.

Some of the 38Zr's previous to 2009, built with 525's came with "shorti" lower drive units. With 1/3 tank gas (60-75 gals) they can go 93mph. If you run with over 1/2 tank
(over 100gals) the center of gravity changes some forcing more trim and causes overreving wasting power (watch for the rooster tail). The more gas in the tank the worse it gets. (I imagine you may have shortis and were running with about 3/4 tank)

Try running with 70 gals of gas to see if what I'm saying is BS. It won't cost you a thing. When you find it's not BS you have 2 options: 1) Run with 90 gals or less, 2) Use longer lower drives combined with new props to match (You'll dig more and can trim approprietly).

Good luck!