Pitch/cup/rpm question

[Rickysa]

Bear with me folks...I know this has been discussed a bunch but I couldn't find the old thread, so here goes.....

Finally got the starboard engine injector issue resolved (new mechanic...the engine was grossly out of tune after majoring)

WOT we are getting just under 2100 rpm...earlier this year (before majoring the engine) we had the props pulled and tuned. What I thought was 26 x 28 no cup was actually 26 x 26 light cup...previous owner had taken 2" out.

Now she is slooooooow getting out of the hole, before the engine work we were getting 2200 wot, 19 knots at 2000....now we are about 15 knots at 2000(bottom cleaned last week)

Prop shop says we need to take another 1.3 inches out to get to 2300...so what should our next step be?


ps...45C, 692s

 

[Freebird]

Call General Propeller in Bradenton, FL. I don't have their number, but if you do a search for General Propeller, their toll-free number will pop up. These guys know their ship.

 

[Paul45c]

What I thought was 26 x 28 no cup was actually 26 x 26 light cup...previous owner had taken 2" out.

Now she is slooooooow getting out of the hole, before the engine work we were getting 2200 wot, 19 knots at 2000....now we are about 15 knots at 2000(bottom cleaned last week)

ps...45C, 692s

I've got your same boat. I presume the props you're talking about are 3-blade. They came with 3 blade 26x28 Nibrals. I'm using mine for spares, but the last time I had them on, my 500hp 6v92s were making right around 2300. There was no cup in them.

I'm gonna say if you're down to 26x26 on 3-blades and still not making full rpm, you've got more work to do on the engines. My 4-blades that I keep on there full-time are 26x26 and change, and they have a lot more disk area ratio than the stock 3-blades above, and I've got no prob making full rpms.

If you're sure your fuel filters & air filters are clean, you're confident of the tuneup, then maybe next step up is to check fuel pumps. The first sign I had of mine getting tired was poor acceleration out of the hole. It made a dramatic difference with new fuel pumps. Good luck.

 

[Rickysa]

Thanks for the response Paul...I wasn't sure if we should be looking at engine things or prop things.

My understanding was new filters were put on prior to sea trial yesterday (the Fleetguard system is in the box in the engine room waiting to be installed this weekend )

Hopefully we can track it down and get back to 26/28 props

 

[Boss Lady]

I would check to make sure that you have the correct injectors for the HP designated. Depending upon which shop did the rebuilds (trucks vs marine), I have seen them look at the book and pick the stock injectors for a lower HP engine. Just because they were in the engine when you got it, doesn't mean they are the right ones.

 

[Rickysa]

I would check to make sure that you have the correct injectors for the HP designated. Depending upon which shop did the rebuilds (trucks vs marine), I have seen them look at the book and pick the stock injectors for a lower HP engine. Just because they were in the engine when you got it, doesn't mean they are the right ones.

Chris,

I was so frustrated with the whole injector thing that I tracked down who maranized the engines and ordered the "all-new-parts" injectors at $300 a pop, which fortunately we didn't have to use, as it was a timing issue. I'm going down this weekend since ernesto is going right over my roof Fri. and will pull the filters, try new fuel pumps, etc.

 

[Paul45c]

Hate to see you have to go through the detective work, but it's so important to get it right with diesels. And clearly the engine is the place to start, whether it's making all its power or not. Once you eliminate the engine, the rest of it is really straightforward.

I guess one last thing to check, while you're at it...the fuel line pickups in the tanks. If they're sludged up, it'll be the same as having dirty filters as far as flow restriction. I'm not sure of the history on your rig as far as how long you've had it and what you've had done, how much you've used it, etc., but if the boat has been run less than 100 hrs./year down here in FL and the fuel tanks haven't been polished in more than 3 years, maybe that's a good place to start. It's one more thing that can be eliminated, and it really doesn't cost much. You can even do it yourself, but if not, the guys who do it set right up on your dock and they're easily done in a day. While they're in process with the polishing, they of course would check your pickup filter screens.

Good luck.

 

[Genesis]

I've got your same boat. I presume the props you're talking about are 3-blade. They came with 3 blade 26x28 Nibrals. I'm using mine for spares, but the last time I had them on, my 500hp 6v92s were making right around 2300. There was no cup in them.

I'm gonna say if you're down to 26x26 on 3-blades and still not making full rpm, you've got more work to do on the engines. My 4-blades that I keep on there full-time are 26x26 and change, and they have a lot more disk area ratio than the stock 3-blades above, and I've got no prob making full rpms.

If you're sure your fuel filters & air filters are clean, you're confident of the tuneup, then maybe next step up is to check fuel pumps. The first sign I had of mine getting tired was poor acceleration out of the hole. It made a dramatic difference with new fuel pumps. Good luck.

Gigabite had 26x25 3-blades with a #2 cup on them - 500HP 6V92s.

The cup makes a significant difference in slip and getting the power to the water. It also makes a significant difference on what RPM you can reach!

26x28 is too much wheel with any cup at all, and you want some for efficiency purposes. 26x26 is ok if you don't run heavy often, but if you do, they're borderline.

26x25, cupped, is a good compromise on that boat.

BTW, if anyone needs a spare set, I've still gone one - tuned and ready to rock and roll. They're 2-1/4" bore but I also have the shims and slipper keys to work with a standard 2" shaft on these boats.