What's the ideal surfing RPM of a EX343?

[JohnnieMo]

I have been invading other people's threads asking questions like this, and I think it's probably worth it to stop that and just ask directly.

I run a 2013 Z1 Vx with the EX343. Right now I am running a 1433. Ballast is about 800 front, 1600+ rear with suck gate. Currently, depending on ballast, I top out around 3500 RPM.

What I'm finding is two fold - first, when my ballast gets to a certain point (about what I described above), the boat has a hard time reaching surf speed. In some cases, it develops a bad vibration (usually if there is a bit of chop). I took the boat in to the dealer three times last year to remedy. The first time they said it was the distributor, so it was replaced. That didn't fix it so I took it back and they conducted an alignment. That didn't work so I took the prop off (that they had repaired previously) and got a third party to fix it. He said it was a disaster. He repaired it as best he could. The vibration got better but still occurs when the boat is at max.

So I'm sitting today with a question about re-propping again to get even more out of this engine/hull combination, while hopefully removing the vibration. However if I jump to something like an Acme 1873 or a 2079, my RPM will likely get up towards 4000RPM. I read the manual for the EX343 to try and determine an ideal RPM range. All it said was 5200 RPM was the max. I also tried to find the torque curve on that motor. I know it peaks at 430 ft-lbs, but I'm not sure what the band looks like.

So I guess my question is - what is the most prop/RPM I should safely run on this combo? Also, is there another place I might be able to find this vibration.

I rode on szklaruk's Z3 last week and his engine is the same as mine. When his 1235 hits a wall at 3500 RPM, his boat doesn't shake. It just does what it can, then stays there happily.

[bsreid]

I’ve got a 1433 on my r20, about the same amount of ballast, taps 3 and I have no problems holding surf speeds at just of 3000rpm depending on crew size.

Is your suc gate putting tons of drag on the side of your boat? When we were first dialing things in the tabs weren’t working properly and it was just a mess to get up on speed. Changed prop and fixed issue and it works great.

[Germaine Marine]

I would measure the difference from the top of the blade to the hull of the prop you currently have. Lets find gap and figure how big of a diameter prop you can fit underneath there. I think you are good to go as close as half an inch with that motor.... Once you set in on the biggest diameter we can figure out the correct pitch and cup to get you on the right track...

[JohnnieMo]

I would assume a suck gate has more drag than TAPS3... not a lot, but some. Depending on the water I can get down to 3200RPM. In general I find the suck gate does better in smoother water as compared to the listed setup. Listed works in almost anything.

I'll take some measurements tonight and get back to you elevated! My guess is that 14.5" is the most I can get on my crappy Boatmate trailer.

[IDBoating]

LOTS of variables in that question, I'm not sure there's one correct answer. Here's my data to stir into the mix.

2009 24Ve (big boat), plenty of ballast (3000+ pounds aft + 400 pounds bow), EX343 (same engine), either a lot of people or an extra 400 pound Fly High sac, 1235 prop, cruise control set to ~11 MPH depending on rider. Engine RPM's are always right at 3000. When actually surfing, fuel consumption is in the 8-9 GPH range.

[JohnnieMo]

LOTS of variables in that question, I'm not sure there's one correct answer. Here's my data to stir into the mix.

2009 24Ve (big boat), plenty of ballast (3000+ pounds aft + 400 pounds bow), EX343 (same engine), either a lot of people or an extra 400 pound Fly High sac, 1235 prop, cruise control set to ~11 MPH depending on rider. Engine RPM's are always right at 3000. When actually surfing, fuel consumption is in the 8-9 GPH range.

Fascinating. Are you listing or evenly weighted with gate? I am going to try out a 1235 here soon just to test it out. I'm not sure how much the added circumference will change things. But I do want to get a prop that is in factory condition so I can at least determine if my propeller is actually "broke".

I hear a lot of people reporting surfing with far more ballast than me and 3000RPM or less. That's just not even remotely possible with my current setup for some reason.

[dj2]

I have the 360hp in my RZ4 with 2000# rear and 400# up front, usually 6-8 adults on board. Evenly weighted, Ronix wedge, 1235 prop and I am about 3100 RPM at 11.5 mph

[talltigeguy]

I think your propeller is 'broke'. Inboards are terribly sensitive to the propeller being off balance and now that you have a prop that has been fixed twice, it would not surprise me if you have something a little off with it.
I think that will solve your vibration issue.

I think the 1235 has been one of the best selling props of all time because it has terrific low end and not too much loss on the top end.

If I am reading correctly what you are saying, if your buddy is weighting his boat and cannot get past 3500 RPM, he is lugging it down quite a bit.

Maybe some gear heads can chime in better than me, but the only advantage to lower RPM's is fuel economy. I don't think it will hurt your engine to surf at 4000 RPM if you had to, as long as you change your oil. On a side note to draw upon the limited comparison with road engines....50 hours would be equivalent to 3000 miles in your tow vehicle if your average speed were 60 MPH. So we change oil quite a bit more frequently in these boats than in our road vehicles. Between stoplights and town driving, 50 hours is only 1500 miles in my truck. And my boat does spend time idling and going back to pick up my rider, so a large percentage of the 50 hours of engine time is not even under load.

[chpthril]

Lower RPM, such as going with a larger prop, is not always the way to go. Need to be mindful of getting the rpm too low and the engine out of its ideal power band.

With my past hands on experience, tge trailer has been the driving force behind prop diameter on the Z1. If the trailer allows, I think a 14.5 is a good dia for a loaded Z1. Theres a couple good options in the 14.5" dia. This will drop the rpm a little compared to the 1433, but not too much.

[Germaine Marine]

Inorder to accurately give you the best advice. Your Drive ratio etc needs to be listed. I am guessing its a 1.5-1. If thats the case, and your trailer allows, I would try and squeeze a 15 inch diameter prop underneath. Lets then set the pitch and cup where it needs to be to keep the motor happy. The benefit of the bigger Diameter (within reason of course) is that allows for a more efficient transfer of power to the water. There is a obviously a limit within each motor and drive ratio combo. I cant see a reason for going anything other less then a 15 inch diameter prop if you have the room and have the 1.5-1 ratio.

Food for thought...... For every 40 thousands you add in cup it is essentially like adding 1 inch of pitch. To a point, you can go this route and not really give up any on the bottom as the change in cup really isnt felt until into the power band and on plane.

[IDBoating]

Fascinating. Are you listing or evenly weighted with gate?

Listing only. TAPS2 single center tab.

I am going to try out a 1235 here soon just to test it out. I'm not sure how much the added circumference will change things. But I do want to get a prop that is in factory condition so I can at least determine if my propeller is actually "broke".

The 1235 made a HUGE difference compared to the factory 537. We've kept the 537 as a backup but we've never installed it since the 1235 showed up.

[JohnnieMo]

The answer is 1 1/8" from the hull. Little less than 1" to the prop guard.

[bait28]

The v-drive should be a 1.48 PCM connected to a 1:1 PCM transmission


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[killerbren]

Johnnie I have a 1235 you can try, you can grab it next week.

[IDBoating]

Johnnie I have a 1235 you can try, you can grab it next week.

Do this! It will answer at least two questions: Is your prop the source of the vibration, and whether the magical 1235 prop will give you the overall behavior you're seeking.

Awesome offer, killerbren! I love how this community supports each other.