4788 with 370s prop pitch question-gctid387087

[Guest]

I am getting my props scanned and was thinking of having them pitched to 23 from the 24 inch that they came with. Has anyone else done this?

I am repowering my boat with reman 370 after a engine failure:sorrow:. When I purchased the boat it had a 24.5 pitch on the failed engine and 22.75 on the other.

I have the good engine for sale in classified for $6,000. Fresh water with only 675 hours.

Thanks for the help.

[WhiteRockMike]

If you have a reasonably loaded 4788 you'll probably need to go to 22 to 22.5" to achieve rated RPM plus a bit at WOT.

[ksanders]

We went to 22" when we repowered. Our pitch is about right. We can make wot plus a little.

Our engines are 330's.

Youd rather be under pitched than over propped. The only thing wrong with under propping is a slower fast cruise speed.

[Guest]

No info on the prop question, but, do you have any idea why the engine failed?

[Guest]

We recently purchased a 2001 47 with 370s, and repitched the props shortly after we got the boat. Here are some numbers for comparison.

Before re-pitch:

24x24 4-blade props, 2835 rpm at WOT, 23 knots max speed, with 8 adults on board, 240 gal fuel, water tanks approx half full.

After re-pitch:

24x22 props, 3160 rpm, 22 knots, with 6 adults aboard, 440 gal fuel, water at half.

Taking 2" of pitch out of the props allows us to reach max rated rpm (3000) plus about 5% (3150 rpm total), which seems to be an accepted rule-of-thumb value. We lost less top speed than I expected, but we really don't plan to travel that fast anyway.

One other bit of information to attach to these numbers is that the boat has underhulls.

wkcarroll

Ulysses

Anacortes

[MalNSF]

What is the downside of over propping?

I checked it yesterday based on the dash gauges at WOT we were about 2900 - 2950 rpm. . We have a zodiac yacht line on the fly bridge with a 30 horse outboard (total weight about 750). We just stocked up for summer so there is a lot of water, soda cases, swim toys etc on board. There were two of us. 380 gallons of fuel and water over half full.

Most of the time we travel at 1500 RPM up in the delta. To and from the delta at the beginning and end of summer we cruise at 2400/2500 rpm.

Based on how we use the boat, is this something I need to have looked at urgently or could it wait for winter?

Cummins 370's.

Thanks for any advice

Jeff

[playdoughted]

Jeff - when we bought our 490, I made the cummins mechanic go back and get his optic tach before we when on the sea trial. The dash tachs were way off and the boat overpropped. First two thing I did when we got the boat home was to buy an optic tach and take 2" out of props. Hope this helps. Ted

[ksanders]

MalNSF wrote:
What is the downside of over propping?

Overpropping is probably the leading cause of premature failure of marine diesel engines.

Here's a link to a pretty good article on the subject:

http://www.mvdirona.com/TechnicalArticles/DieselEngineOverload/AvoidingDieselEngineOverload.htm