For smart guys and gals and problem solvers

[Bigsfish]

Thanks Jeff. Yes Cummins is the only prop source.

 

[Wxx3]

The problem came over the first year and a half as more stuff was put on the boat and appears to have gotten slightly worse lately.

Unless you just want to spend money to spend money, then it seems from my slow-assed perspective, to do what most have said and take weight off.
Yes, even if it takes you a few days.

Wait, spend 1/1000th of the money you are willing to re-rate the engines (which by the way does exactly what it says, and it don't say "go faster") to to HD or whatever big box stores people hand outside to work and hire a few guys to do all the heavy lifting.

As Ski and B&B have said a few times, before you go chasing dollars, go back to square one.

Your post above pretty much is telling the the issue.

Don't ignore your OWN observations.

 

[smitty477]

Bigsfish,


The weekend is coming up and perhaps there is a way to get some reasonable data without too much time or inconvenience.
In another post I think I remember that you have a large fresh water supply as well as a large holding tank capacity - if you combine that with your dinghy and a short trip with a 'bunch' of volunteer friends maybe you can get some confirmation without too much work.
Is this possible?
- Empty the water tank(s), pump the holding dry, drop the dinghy to the dock temporarily and take the boat out for a test run with one extra person and record your numbers carefully at WOT as well as a few other cruise points. I have used a digital camera to take a shot of all my gages in the past for this purpose but also have used preprinted sheets to fill in the desired data. This trip should not take long at all.


- When you return to the dock add back the dinghy, add back all the water as well as filling the holding tank with water (maybe 450-500 gal in your case). Get a bunch of people to join you for the next 'cruise' and copy the same tests you did above. The difference in weight should be in excess of #5,000 and the results will show how significant the weight gain is to the speed and rpm as the boat stands now.
Perhaps this will give you most of the feedback you need without the necessity of lugging off all your possession's , waiting for fuel changes, and removing and replacing 1,600# of lead.
I have had good results with this in the past - the only downside I have had was when I asked a young lady on the 'cruise' what her weight was. It of far better to not ask and just take a reasonable estimate.

 

[smitty477]

It is likely worth noting what I would do if it were my boat as I have followed this path in the past.

When the boat was new and stripped of all the weight, had a perfectly clean bottom and running gear and was the 'fastest' it was ever going to be it reached 3,350 rpm.
In my case with mechanical diesels I would have wanted to rep-itch right then to get to at least 3,500. It would be an unknown how much rpm would be lost due to added weight and time so loading up the boat with 'extra' weight as best you can when new is one way to simulate the gain later on.
Here we have an electronic diesel where the ECM will not let the rpm extend past the high rated 3375. But in my opinion and what I have practiced in the past is to aim so that full 3375 would be reached when this boat is fully loaded, on a hot and humid day, and with bottom and running gear conditions that are likely to be in place during use (not perfect). For those reasons it is always best to pitch the props less aggressive than what you may originally think.

 

[Bigsfish]

Smitty

All good suggestions and I do believe weight is a major factor so my plan is to have Cummins do the normal service on the engines and look for anythiywhich may be keep them from turning up. Clean the bottom and drives and see what happens. The problem is I want the stuff on the boat that's there so I will probably have to reprop to get a couple of 100 rpms at WOT. At least that's what I'm thinking.

Thanks.

 

[smitty477]

I have seen problems similar to this on over 2 dozen boats between 38 and 47 feet mostly Bayliners but some Sea Rays as well. Most were Cummins 6b or 6c but a few Hino's and a Volvo or two in there as well (all 6 cyl turbo, 4 strokes in heavier cruisers)
In every case where loads were added the less aggressive props made a huge difference and actually added efficiency, engine longevity and top speed. The email responses I have over the years include some charts and data that was surprisingly positive even from my best guess at the time.
In any case - unless you have a true engine problem requiring attention or poor boat hull conditions the results have always been very positive over the past 20+ years.

 

[Bigsfish]

Smitty

Thanks, I hope I will continue that trend of success although Murphy and I are first cousins. ��