top speed on 18" Lund

I don't seem to match what others are claiming on an 18' 2002 Lund Fisherman w/ 150 Hp Merc EFI V-6. I have a 14"X17 pitch prop but only get 43MPH and the RPM is only 4900 WOT at an altitude of 3200'. I should be 50 MPH easily and I am running light. I am new to this rigg and expected more from it. If I drop the pitch I will loose even more top end speed. My motor also growels when I back off wide open. Does any one else expierence this?
Thanks for your input, Muleskinner

Re: top speed on 18" Lund

im no expert but .....
a few things to check....
1. the weight of the boat against manufacturers specs,
2. your leg gear ratio. have a real leg mech that knows the type look at it.
3. a different style of prop. 14 seems very low for a v6 4.3 my guess is a 19 would be about right. thats why the gear ratio is also suspect!

was it a new or used boat?

Re: top speed on 18" Lund

I,m running a 2004 Merc.150efi on a 2001 Tracker Q3 ski & fish. My rpm is 5400 (= or-200) at 55-59 mph(21P Trophy plus prop) depending on temp and humidity.My boat is glass and yours is Aluminum I would think it would be faster?With the prop your running i would think that your rpm's,would be a lot higher. How long does it take to get on plane and when was the last time you de carbed and replaced the plugs? Sorry oops this is not an io but a ob, hope this helps muleskinner, P. D.

Re: top speed on 18' Lund

Re: top speed on 18' Lund

The lund is 2002 18 ft.Fisherman and I only have the prop it came with but I have heard of other guy's who get more speed on their rigs with the same 150Hp EFI Mercury. I put new plugs (NGK) before I tested it. It has a good hole shot but could be a little better maybe. It also has very quick throttle response but low RPM at Wide Open Throttle (WOP). I'm afraid I can't put a more aggressive prop on it to gain speed because it's already running 4900 below the recommended RPM of 5000-5600. I played with the trim and the top speed is only 43mph and thats with no gear and one passenger and no wind.This is nuts!

Re: top speed on 18" Lund

Thanks for the replys. Oops , what do you mean by an leg gear ratio. I'm sure everything is stock and nothing was changed. I agree that a 14 1/2" prop seem too small for a 150 Hp and the prop has no damage.

Re: top speed on 18" Lund

14" + props are designed for the normal 150 hp gearbox.

I am a sea level (more or less) guy. Last year I went to New Mex. and Ariz. and at altitude my trucks performance was much less than stellar. Altitude really did a number on my performance.....same applies to marine engines.

Suggest you get some local numbers for determing what your performance should or shouldn't be at your altitude. Your numbers seem like your 150 is only putting out about 90 hp and it all could be due to altitude.

Just ran some prop calc numbers and your numbers are reasonable except for the 4900 part which translates to not enough hp to get the performance you expect from your 17P prop and (1.87 gearbox) and I'm going to bet it's because of altitude degrading your hp. If I'm right, you are going to have to go down in pitch a couple of inches at least (200-300 rpm per inch = 5300 to 5500 rpm at WOT; engine rating 5600 max WOT and folks on here prefer top end running at max rating.

Mark