performance and bottom paint removal??

[seastrike]

I have a 78 20 foot master angler. Motor is a 150 e-tec. Boat has trim tabs. I am having the bottom paint removed, an was wondering what yall think this boat should do with a slick bottom. In the past with 2 people and a full tank it would do about 38-40 mph at 5500 rpm,depending on how high the seas would let me trim the motor out. With the new slick bottom what kind of increase should i see. Will it now turn more rpms with a slick bottom, i wonder if i'll have to adjust pitch or get a new prop??

[McGillicuddy]

Interesting. Some anti-fouling bottom paints actually reduce friction by letting air between the hull and the water giving the boat some separation and thus less friction. Assuming the motor is in tune and your fuel is fresh, I would consider a couple of other things before blasting the paint.

If your mph was actually knots, you're probably fine; if indeed your reading was mph, that seems a little low for a 150hp E-tec. You might check your motor height (anti-cav plate should be about 1-1/4" above the bottom of the keel when the two are parallel). If it is too low, it will drag and reduce performance, sometimes dramatically.

How big is your fuel tank, 40 or 70 g.
Also might identify your prop model which may help one of the prop wizards to determine if the model of your prop and its geometry's desired effect is right for your boat.

Good luck with your MA

[seastrike]

bottom paint is already coming off,,,it was pretty rough you look at it and tell it would affect performance, boat probably had 10-15 coats. It needed to go

[McGillicuddy]

Roger that, seastrike - 30 years of bottom paint = drag. I have a smooth unpainted 20' Seafari hull and get 36 mph at 5500 rpm in flat or chop with an old unmodified in-line 6 Merc 115 with 40 gallons of fuel 20 gal. Bait tank and 500 lb riders. Gotta believe that e-tec can do much better, still check those other issues when you can...

[Seacraft84]

That seems about right for the speed. You may gain a little (1-2mph). I had a 23' that I soda blasted but redid the whole boat and ended up gaining 3-4mph after the restore with the same motor.
I now have a 20MA with a 175 Johnson and runs 42-47mph depending on conditions. Also has bottom paint.

[Fr. Frank]

That speed seems pretty low. With my heavier 20' Seafari, running an re-manufactured '92 XR4 Mercury 150, I had a top speed of 53 with a light load, and 47-48 mph with an average load. And yes, that was with 3 heavy coats of Petitt "Trinidad" bottom paint. The difference was motor setup, tuning, and propeller selection.

Having once made a living in part by rigging and tuning high performance pleasure boats, I know the difference in performance between a well-rigged boat and a "default" dealer rigging job can be a 20-25% loss in optimum performance and economy. I made a lot of money off people who bought new boats from a dealer just by promising to deliver 10% more speed for an additional 10% of their purchase price. I never failed to deliver that 10%. Never.

Bottom line is that you should be getting 43-45 mph at a minimum, even with really rough bottom paint, and close to 50 mph with a smooth gel-coat bottom. (Blueprint the hull, rig properly and with that motor you could probably touch 53-54 mph, as long as you don't have a top.)

If you're not getting low 40-s for speed, you need to adjust the motor setup and most likely the propeller choice. You're not properly rigged and set up.

[Bushwacker]

Interesting question - I'm currently doing the same thing! I recently had the bottom paint soda blasted off my boat and am currently cleaning it up and repainting with Interprotect and Signature Finish paint. I'm hoping to get about a 10% improvement.

I've seen 44-47 mph on my Seafari with a 150 E-Tec running a moderately heavy load with the bimini top up. This was with a 14.125x20P 4B prop that's only turnning about 5000 rpm, so I'm pretty sure it's far from optimum. I have seen almost 50 with a light load and top down. The bracket has 30" setback, and may add 2-3 mph; cav plate is about 3.5" above keel. The boat had 3 coats of bottom paint that had been on it ever since I got it in 1975, and a lot of it had pealed off clear down the the gel coat, so I'd say it was fairly rough. I'm about a month away from sea trials with new clean bottom, so will keep you posted.

[Seacraft84]

Forgot to add that I have a T-Top.
I think I may be able to raise the motor a hole up and maybe gain 1-2 mph also.

[seastrike]

thanks guys,,,when i get the boat back, i will take pictures of my setup,get some measurements,check my prop, and we will definatly revisit this. I'm kinda like yall it seems to me i ought to easily get 45-mph