28 250 cummins prob selection

[bktuna]

Hey Guys,

Just bought a 28' with twin 250 cummins, I got 2 sets of props with the boat. WOT I am turning 2900 rpms @ 26 kts, I know these engine WOT should be around 3050 3100 rpms... Help me figure out what I should do I beleive the wheels on the boat now are 17 x 21's ...

[Capt B]

If you do a search, you will see quite a bit of discussion on this topic. I have the same configuration and have 17 x 20 Acme props with a .075 cup.

[CC28_NJ]

I too have the same set up, was having a hard time turning over 2800. My boat is on the extreme heavy side, I probably store too much gear on her, with the addition of the tower genny,ac, etc, etc, First thing I did was verify throttle linkages/Cables, this WILL effect WOT, as I have found out, I was out one day, in a pretty strong head sea, probaly 4-5's, and could not get the boat to plane right, and only hit WOT of 2500, This was not acceptable by any means, so I started doing a lot of research, and spent many good fishing saturdays's tuning her up.
- First thing after you verify your linkages, check your entire sea water system. Starting with the sea water pumps back, Clean and check your aftercoolers etc, My port engine, which was would only turn 2850. has a lot of calcium built up in the trans cooler. Bascially just flushed these out. I did take apart the aftercoolers and clean them, but I really didn't have to at this time, Just check for blockages.

-Make sure your air filters are clean, and a turbo flush wouldn't hurt.

-Next thing was I got rid of my Racor 900's, and installed a multistage fuel system. (optional but recommmeded).

-Next I pulled the boat 4th of July weekend (I was dedicated to fixing this issue), and cleaned the bottom, making sure the strainers were clear, ran new trim tab hoses, as I had 2 blow apart on me, and this boat WILL NOT plane without tabs. And Finally installed those Magic Acme Props.

Boat now will reach 3000, Would like to get more, but Happy hitting 3000 right now.
The Acme's do what they say they will, very nice performers, Boat definitly gets out of the hole faster, less bow rise, and right now I'm crusing 2500, about 25-26 knots. At WOT the other day I hit 33kts.

I had some other issues which may have attributed, sea water pump on starboard engine was leaking, replaced it, I had an excessive steam issue and this cured that problem. Impeller on port engine was tore up, this was also lying in one of the coolers.

Without rambling on anymore, basically look everything over for obvious signs, of something holding the engines back, might not be the props.

My issue was I believe when I bought the boat, the guy just didn't want to worry about it the last year they had it and just let this stuff go.

By the way, As much as I like the ACME's I don't believe Props were the reason my boat was not performing right. attributed to it, but not the main issue.

[bktuna]

I am new to desiel boats and I love my CC 28' compared to my Boston Whaler I had before. I am in the process of learning the systems and making sure everything is in order... I know 2 things for sure the props on the boat now are 17x21, and I am not getting 3000 rpm at wot. On survey the desiel mechanic said i should def change props to get the rated wot rpm's for the engines (3050-3100). They are small engines but I have heard if you take care of them they will treat you good for a while! Thanks for the help and anyother feed back is appreciated.

I have an extra set of props that came with the boat I believe they are Hy-Torg, I was thinking of getting redone to get my wot rpm, any suggestions 17x20 with .75 cup?

This weekend ran offshore, fully loaded with gear, 4 guys, ice, full fuel, tower, genny, ac/heat. Going out ran 2400 rpm @ 20 kts, but this was before I learned that I should run th eboat at 2600 rpms. I pushed to 2500 rpms but still was only doing @ 21 kt. On the way home with no bait and a little less then 3/4 fuel ran 2500 and made 23kts in flat seas with a slight follwing swell. WOT 2850 -2900 @ 26.4 kts, I am going out today to run the boat and take notes and figure out whats going on...

How do you guys run the tabs, I found that with no tabs bow down she eats up a sea, 1/4 -1/2 tab more speed but she will bob up and down more... any suggestions...

Like I said I am new to running a boat like this but its all a learning process, so any comments will help...

[biteme]

props

bktuna if you bought that boat on eastern long island we should talk....

[bktuna]

why??? I bought it up in MA,... But email me your number anyway id like to talk i believe you use to have the same set up as mine... [email protected]

[biteme]

props

sent you my #.

[bktuna]

Hey bite me didnt get an email, email me again please at [email protected]


Went out today, 2400 23-24 kts, 2600 [email protected] 26.5 kts ( no tabs) brought the nose up a little and had 28 kts.... This was all going with the tide... WOT had 2850-2900 rpms @ 28.5 -29 kts

I am def not turn WOT at 3050-3100 rpms... going to try and adjust the props...

[biteme]

props

you have to get the wot rpm into the correct range for the engines to run as designed but remember when the props are adjusted to bring your rpm up (less bite)your boat will slow down a bit....Charlie

[bktuna]

Yes this I understand but they pay off will def be less strain on the engines, and have them run to factory specs.

At 2600 I want to be able to cruise 25 kts. w/ having the engines meet proper wot rpm's Mac says this is were the boat should cruise at that rpm

[Capt B]

Are these speeds on a GPS (speed over land) or on a wheel on a fathometer?

[bktuna]

Capt B., at the time of the test I had 3 different machines on. Navnet, Radar, and northstar, as well as fathometer. all the machines were with in .2- .3 kt margin of error. Sometimes there were perfect insync. and all reading off different antenas.

Founturnatly, there is a Prop mgf. a couple blocks from my machine shop. My father stopped in , and after a quick discussion and an offereing of our custom CNC trolling heads, he is going to help change our spare props and figure out the best prop configuration with these engines.

[biteme]

props

what year is your boat.cummins had problems with injectors failing on these engines..find out the service history on your boat.unless your props are damaged they should be rite for your boat if they have factory settings...injector issues can steal power causing the same symptoms. check your oil for fuel. do they smoke a little more than normal..did you buy the boat from a dealer or private?...Charlie

[bktuna]

Its a 2000, with 250 cummins, the engines had 620 hrs on them. I bought it private from through a broker in MA. I know that had issues but I beieleve they would blow in the first few hours of the engine...not black smoke why running which would be caused by injector problems. The cummins survey mechanic said they were fine, above average and he was a nuetrul party

[Qman]

Cruising speed and injectors

I have a 2001 28 with twin 250b and once I get over 2400 my rpms almost match my speed. Loaded I cruise between 2400 and 2600 at speeds from 24 knots to 26. Its been a while since I went wide open but if I remember correctly i hit somewhere around 2900 rpms with a max speed around 29 knts.
Very happy with performance. Also as far as injectors go I did have mine recalled about 4 years ago so maybe yours where never done.
Hope this helps