1987 Mariner 90

[junkyardwarrior]

I have an 87 model Tidecraft V15 bass boat. I believe it is 15'6" length. It has a 87 model Mariner 90, with a Quicksilver 48-72500A5 21" prop--I do not know the diameter (I believe it may be a 12 3/4"?) No jack plate and the engine is mounted in the second hole from the top (moved up about a 3/4" or so). Top speed is about 48 with me and my fishing gear. I would like to "tune" this thing to achieve the absolute best top speed that I can, without spending a ton of money. I may buy another prop in the future if I need to, for running across the lake with 2-3 people in the boat. Maybe a cheapie 4 blade prop to get it on plane easily.

Anyway, mine does not rooster tail at all. Most 'glass boats I see make a smaller tail. I currently do not have a water pressure gauge-though-I will be getting one soon. Even trimmed all the way out, it just seems like it should be a little faster. With everything out of the boat (seats, trolling motor, batteries, gear) I can get 54 mph on slight chop. Smoother water is slightly slower. It seems like I should be able to trim it further. Any insight on this?

Under the bracket, there are a couple of seats where the trim rods ride. I shimmed them toward the front of the boat to trim the motor a little more, and it helped (from about 46 to 48 mph). Also my prop does have a couple nicks in the edges (rocks, etc) but it is not severe. I filed them to match the rest of the edge as best I could. Is that prop any good or are there better choices? Aside from buying a jack, is there anything else I can do to help?

 

[sschefer]

Re: 1987 Mariner 90

If at top speed you are maxing out the RPM's, (manufacturers spec's on an unmodified engine), and you still have throttle left you can increase your pitch and gain more speed. The opposite is true if you aren't reaching max RPM's at full throttle.

A hydraulic jack plate with a 4 inch offset could get your prop into cleaner water and trim tabs are definitely an easier way to get your boat on the correct plain consistently. The hydraulic jack plate will allow you to raise and lower the engine height about 5". That might help you find the sweat spot.

Seriously though, a 16 ft bass boat with 90 hp engine doing 50+ empty is not bad. Most certainly your speed will increase as the day goes on and the gas goes out.