Boat not as fast as it should be.

Question

I just purchased a 28' Seamaster cabin cruiser. 7.4 mercruiser motor, The boat was a great deal. The boat is pretty slow. I can see barnacles on the hull and prop from lack of use. I do believe it may not have the correct prop. Any Input would be greatly appreciated.

Answer 1

Exactly how slow? The barnacles and slime affect the speed. If/when you have it hauled out, they can leave it in the slings and power wash all of that off. It usually costs around $200-250 depending on boat size. Don't buy a new prop. There are so, so many factors involved that you will be totally wasting your time/money. What you do need to do is document (you'll never remember all of the info) your speed at various rpm's. Try to keep the conditions equal, wind, current (could slow you down 4-5 knots), fly bridge windows open or shut (1 knot min), water, fuel on board, etc. Then have the bottom cleaned. Compare notes. Determine top RPM that your engine will get (you will need that info if/when you buy a prop) at wide open throttle.  While the boat is out, inspect your prop. Look for dings. Also, document the  diameter and pitch of your prop. Numbers should be stamped on the side of its hub. The first number is diameter, next is either LH or RH (left or right hand drive) and last is the pitch of the prop. Having this info, you can research what your boat should have. But dont waste money on new props until you've done the homework. Throwing money at this kind of stuff doesn't usually fix it. Good luck.

Answer 2

I'm not sure if you really mean  a 7.4 hp merc motor, but if so thats like the kicker or trawling motor for fishing at low speeds.

You would need like a 200 or 250 merc

Answer 3

No question, clean the bottom and running gear, before you change the prop.  Check it for bent blades and dings, but I'd bet most of the problems are barnacles and groth on the bottom. Good luck!

Answer 4

A 7.4 hp motor is not enough.  Also, whatever motor you have, you have to get those barnacles off.

A clean bottom is what you need.  You should haul out your boat, have a really good cleaning, sand and put a couple really good coats of anti-fouling bottom paint on her.

The hull can be cleaned in the water, using SCUBA gear, a metal scraper, and gloves.  Do not try to pick barnacles off with your bare hands, they are sharp as razor blades, and will slice to the bone.

Answer 5

its the barnacles. u should get ur boat properly wash and if it is going to be left in the water there is a special paint for the part of the hull that is in the water.  

Answer 6

Any barnacles on the prop or any nicks on prop will affect top speed on boat. First step is to clean and inspect.

Answer 7

Slim on the bottom will decrease the hull speed> 7.4 is border line for HP for that much boat> Clean the bottom check the prop for imperfections> make sure it turns  the correct RPM a wide open throttle with a load>