Bottom and Running Gear Seriously FOULED.... Cost me RPM or MPH???? or BOTH?

[dpvandy01]

Ok so my 2001 280 DA Single 7.4L BIII is having a few issues. I've not been running it as often as I have in the past as I've mostly been running the 185. SO normally I'll get 28 MPH at around 3600 RPM with WOT being in the 4600 to 4800 range.. Well this past weekend it struggled to plane and once it did I was only able to get 4000 RPM. At 4000 RPM my GPS was showing 27 MPH. The bottom and running gear are seriously dirty (lots of growth) since I've been off from the fire house with a fractured wrist and haven't been able to clean it for about 3 months. My question is will growth affect my WOT or just my speed? And another issue related or not but the Drive Gear reservoir which was full prior to leaving the slip was empty and alarming 20 miles later.. I topped it off and checked the bilge but didn't see any evidence of a seriously leak. Additional info,,,, Full Fuel, Holding tank EMPTY, H2O about 3/4. Normal gear, and my wife and myself only. This boat is what I would consider marginally powered as is but it seems something is amiss here. Best case scenario for this boat with a clean bottom is in the 41 to 43 MPH range. So growth accounting for 800 RPM and 14 MPH??

 

[moparlvr4406]

amazing what the loss of hydrodynamics causes isn't it ??
it would be the same as trying to fly an airplane with grass growing on the wings :wink:

 

[trit21]

Yes, growth will definitely account for loss of speed and rpm. Basically the growth adds additional load, lots of load as you have seen. Clean the bottom and I would expect everything to be back in order.

 

[Danny Troy]

At 4000 RPM my GPS was showing 27 MPH. The bottom and running gear are seriously dirty (lots of growth) since I've been off from the fire house with a fractured wrist and haven't been able to clean it for about 3 months. My question is will growth affect my WOT or just my speed?

I sea trailed my new boat (a 2003 280DA) a few weeks ago, and it also was only able to do 27mph wide open, verified on GPS. I went way out on a limb and bought the boat anyway. The engine, a 496MAG, sounded way to nice to have any major issues. A Mercruiser diagnostic report also showed no faults. Anyway, when we hauled the boat out to do the bottom inspection there was a pretty good amount of barnacle growth on the Bravo III duo-props. Also, there was a fair amount of barnacle growth to the rear of the hull. I got the boat to it's new location, with bottom pressure washed, and guess what..... I did 41mph with no problem, and probably could do a bit more than that with some tweaking. A definite sigh of relief, after having spent 45k on the boat. So, yes, that growth can really, really slow you down.

 

[kaz911]

Here is one for you...

SR 240 Sundancer 2007 - anti-fouled - could only do about 3900-4000 RPM. I dived under and found ONE trimtab where the Antifouling was "forgotten" - cleaned it - and got it back to 4650 RPM. Just from ONE trim-tab with growth. The rest of the boat was CLEAN!

My 210 Select had (due to experiments) no anti fouling on it. When power was lost to the experiment for a while - I got about 1 1/2 inch of growth on it. Max RPM 3200 (normally in the 5000 range) - top speed 21 knots vs 41 knots with no carpet underneath. Fuel consumption more than DOUBLE pr. nm. After a good scraping with a Waveblade in the water - and surface "treatment" with Triton Marine hull cleaner - I was back at 41 knots and 5000 RPM.

 

[plumbhappy]

I had had very similar experiances. My old 268 would barely plane and at WOT (3700) it would barely do 17mph. I pulled it out (on the trailer) and inspected the bottom. It didn't look that bad; it had some very short hair, but I decided it was time for bottom paint anyway. After fresh bottom paint, the boat ran out better than it ever had since I had bought it. WOT was 4500-4600, which it had never done before and it cruised at 25 mph with 3600/3700 rpm. It was a huge difference!

I recommend you have it hauled and the bottom painted.

Rob

 

[Woody]

I don't get anything hairy or lumpy growing on my boat. The waters too cold I think. But I do get a very thin coat of smooth slime and even a months worth of that can be noticed in performance. I've learned to clean the boat in shallow water as often as I can, it looks a lot better and runs up to snuff too.