3500 Performance Help

[Pura Vida]

I have a 2001 3500 with twin 7.4 litre Merc's. Wish I had the 8.1's, but that is not the case. The props are 19 x 19 - 4-blade Nibrals. We carry way too much stuff. Big tender. A tool for every occasion. A bottle for any mix, you get the picture. Anyway, fully loaded, water, fuel, provisions for 4 for a week, we have trouble getting on plane and sometimes cannot plane. Trim tabs are working fine, just seem to be 50 hps short or something. Top end is 27 knot fully loaded or not. Top rpm is 4500. Should I re-prop. Any advise appreciated thanks.

[seapuppy]

well...first thing I'd check is the hull to see if it's all crapped up with growth.......then I'd put your boat on a diet...get rid of stuff you haven't seen in yrs...then I'd look at checking the engine for state of tune and THEN....look at the props...are they in good tune.......THEN look at what props to change or to change the pitch or not...that's how your going to get your boat back in the performance range........


SP

[rodrigo]

I have 6.2l's on mine.... it planes fine... I carry a dinghy on the swim platform and a bunch of extras for vacations and I get it to go on plane no problem...not very efficient on gas consumption but it is what it is.... I would try changing the air filter I had a k and n on my old boat that look like a cone,and that made a difference... also change the plugs to Iridium... remember when you change your props to ones with less pitch you might get on plane quicker but you will lose top end speed also your engine will run at higher rpm's and they are probably very expensive...maybe $2k a piece... good luck...

[shrew]

Ditto on the boat diet. Go through every single locker and look at what you have. Do you need every single type of cleaner? How much waxing and polishing do you do out on the water vs. in the slip? If you don't use it, get it off the boat? do you need to run with a full tank of water or fuel? Try cutting back. Gas is a little over 6lbs/Gal. Water is 8lbs/gal. Where is the cooler and dinghy stored? Is everything out back? Do you store gear in the mid cabin? I put my portable generator, dinghy and cooler in the cabin companionway as far forward as possible when I'm running. How many people? I have all passengers move forward while I'm getting on plane. If everyone is sitting across the transom seating with their feet up on a cooler full of beer and ice I will also have a very tough time getting on plane.

[shrew]

Also, 4500 RPM's sounds about right for a 7.4, so I don't think a re-prop is the answer. However, condition of bottom and even the condition of the paint will impact performance.