right prop?

[bluemoon]

I am a new owner of a 1997 cuddy cabin with a Yanmar 240 hp diesel. During sea tests, the WOT rpm was 3100(a little over half fuel load). It needed to be 3300 rpm. The prop size at the time was a 16R20 cupped to #4. I had the prop shop rebend it to 16R18 with the same cup. With full load of gear, I now get 2800 rpm at WOT. Can anyone tell me what they are using, as the prop shop bill will get expensive each time I take it in for rebending.

[SCOOTER]

I am a new owner of a 1997 cuddy cabin with a Yanmar 240 hp diesel. During sea tests, the WOT rpm was 3100(a little over half fuel load). It needed to be 3300 rpm. The prop size at the time was a 16R20 cupped to #4. I had the prop shop rebend it to 16R18 with the same cup. With full load of gear, I now get 2800 rpm at WOT. Can anyone tell me what they are using, as the prop shop bill will get expensive each time I take it in for rebending.

Something isn't right here.

With what you've said, you should be over the stated max RPM of 3300.

What does your prop shop have to say about it?

[bluemoon]

Well, We talked about it and it appeared that a two degree reduction would do the trick. It now looks like about a 13 to 14 pitch is needed. Any idea what the factor is using on new diesel models?

[Kurt]

I think Scooter means that you reduced the pitch by 2" and the WOT RPM fell instead of climbing. However, it appears that you also changed the amount of weight on the boat between the two tests. Did you add a significant amount - approx. number of pounds?

Did the WOT speed of the boat drop as well?

From what I've read, you can't change the pitch of a prop from its original value by more than a few inches without possibly damaging it (cracking, weakening, reduce its efficiency). So, re-pitching that prop to 13" or 14" might just ruin it. I would guess that removing some of the cup might help with increasing the WOT RPM.

There is a new member here, Pitch Perfect, who runs a propellor shop. It might be worth contacting him to see what he has to say. Here's a link to his contact information:

http://www.fishtheclassic.net/forums/showthread.php?t=14383

[Mistress]

Apples and oranges....but with my Cummins and 1:1 gear, I'm running a 16 x 17. Some are running 16x15. I suspect you have a diffent gear, a bit more hp and a bit less torque.

The rpm going down with less pitch would imply something else. Make sure your engine is up to snuff before radically chasing it with a prop.

What kind of fuel filtration do you have and what micron filter? I'd suspect some type of fuel/fuel delivery issue....or possibly a turbo. Does she smoke with the throttle pushed forward?

[Scratcher]

The very first thing to check is your tach to see if it is reading correctly. Ideally you should use a phototach to measure rpms at speeds given by a gps.

[bluemoon]

Thanks everyone for your inputs. The gear ratio is 1.56 and she does not smoke at all. I topped off the fuel tanks and loaded her up to do some fishing. I would say about 400 pounds added since the sea trial. She drop about a knot of speed from 30.9 to 29 knots. I have a racor filter with a 2 micron filter that I had to change do to sludge and nasty stuff in the old tanks from the old owner. I also changed the engine filter at the same time. The turbo charger was clean out also. I can hear the turbo at the upper throttle settings so I know that is not the problem. Is there any way of checking the tach? Can any one of the members that have a 22 wac with a Yanmar 240hp tell me what prop pitch and dia they are using on there boat? It would eliminate one less thing.

[Pitch Perfect]

Something sounds fishy here. Off the top of my head a 200 rpm increase on a 240 Hp 1.56 gear ratio should be around 1 inch reduction in pitch. A wot rpm of 2800 means something went backwards. 400 pounds increase should not effect rpms by much. Sounds like the pitch went to 21.5 instead of 18.
I have a digital tach if you need.
Let me know if I can help.
Chuck.

[Mistress]

Get rid of the 2 micron filter in the Racor and swap it out for a 10 or 30 micron. 2 micron is too restrictive for primary filtering.

Not smoking is good...that's means you're getting enough air to go with your fuel.

Check the tach and swap the filter and report in.

30 knots top end doesn't sound appreciably off.

[SCOOTER]

Yanmar wants a 30 micron primary fuel filter used on their engines.

That 2 micron has got to go!!

[Scratcher]

If there is "stuff" in the tank that clogged up one filter quickly its very likely it is starting to clog the next one too (like Scooter inferred) especially at 2 micron. You can put a bulk separator as the first filter then have your racor, then the on engine filter. This would greatly reduce change times for the racor and the bulk separator is a lot less messy to change out because it is a cartridge type you throw away. The bulk separator I have is 30 micron, so it picks up the big stuff, then I have a 10 micron in the racor, then (I think) the on-engine filter is 2 micron.

There is a good article on this type of stepped filtration system at www.boatdiesel.com in the articles section. If I remember right the bulk separator cost me just over 100 buks and that included a couple of spare cartridges.

Even if it does not turn out to be the problem the bulk separator won't be wasted money, it'll save you a lot of filter changes and give a cheap added layer of protection to your engine.

Be careful to stay within spec if you up the micron size of the filter you put in your racor. If there is crud in your fuel that filter is doing exactly what it should; keeping it out of your injection pump and injectors. See what the owner's manual says you should have for a primary filter, and also double check the on-engine cartridge spec. The injector pump on my cummins goes for about a grand, so its not something you want to have to replace!

A fair number of owners install an electric fuel pump into this type of system. With the electric pump they have an on-board fuel polishing system. They can also pump fuel from the tank on one side to the tank on the other to trim the boat if necessary. When the engine is running even a small diesel will pump up to 60 gallons/hr through the return lines, so a system like this really filters the fuel. Finally, if you want to monitor your system, you put a vacuum gauge next to the lift pump and that lets you monitor the condition of your filtration system. Its all in that article I mentioned.

[bluemoon]

I took out the 2 micron filter and replaced it with a 10 micron filter. There was no change to performance, still 2800 rpm and no smoke. It is either the tach or the prop pitch. I am going to call shamrock to find out what they are using on the new boats for dia and pitch.

[captain2]

I am going thru the process as well. 26' cuddy heavily loaded with equipment. Cummins BT5.9 (210 BHP) Rated at 2600 RPM, Borg Warner 72C 1.00:1 Cummins recomends a 15x15 3 Blade. I was up to 17x17 when the top RPM abtainable was 2200. I just got the Prop back with 2 inches of pitch taken out. Sea trials today will see if I need to start cutting Diameter. Captain2