11 ft boston whaler repower

[madman2021]

Recently picked up a great deal on a 1984 11 ft boston whaler super sport. Came with a 20 hp mariner that's junk. Test ran the boat last weekend with my 1989 evinrude 15 hp. With 2 full sized adults and me(fat azz) it wouldn't plane. Just plowed threw the water at 9 mph. With just me and 1 other person it did 19 mph. Just myself it did 24 mph. Amazing for a 15 hp. Looking to repower with a 4 stroke with power tilt and electric start. The tohatsu 20 hp caught my eye but I'm not sure it's going to be enough power. Weight on that motor isn't too bad. The 25 hp tohatsu is a little too heavy I think. Anyone have one of these with a 4 stroke and have numbers with people on board. It will be used as a tender mainly but will fish the islands when we are out there.

 

[Sea Rider]

A 11 footer boat is not a large one to plane it fast specially if boaters are heavy champs. Too much hull drag for OB to get it out of the holes fast. For that need to have deck weight evenly distributed, correct OB/transom height matched, proper trim as a starter.

In your particular case, you boat with too variable load and that issue kills wot rpm along plane. Prop right whichever HP plan using to run full wot revs with min 2 up (boaters you usually go boating with) for combo to achieve a faster plane with slight top end speed loss.

Will need to install an induction tach meter for that task in order to play correctly with less pitch props along add what was suggested in the first paragraph. Most OB's factory delivered with a prop comes usually over pitched and need to have a prop maximization for each current application as each boat/engine model is a unique installation.

Happy Boating

 

[racerone]

Take the boat over a scale and weigh it.----It could well be that foam is waterlogged.-----Or post pictures of boat floating in the water.

 

[Scott Danforth]

35 year old whaler... Check weight, also guessing its waterlogged

 

[madman2021]

Its definitely not water logged. Can pick it up easily with 2 people.

 

[Sea Rider]

Before going for a larger OB, would it be possible to prop right current Mariner 20 HP-OB to run at max wot rpm range factory stated ? Will need to make sure OB is running strong before going for a prop maximization.

Just hate it less and see if can better its water performance to suit better your boating requirements.. If hull is completely dry, it's under powered, lacks punch.

Happy Boating

 

[madman2021]

Mariner has a blown lower unit and low compression. Not worth fixing. Only interested in a new 4 stroke with power tilt and electric start. The 15 hp evinrude is my hunting outboard.

 

[Sea Rider]

If going for the 20 HP Tohatsu OB install an induction tach on dashboard and once break in period has ended go for a prop maximization for 2 up for OB to run at least middle to max wot rpm range factory stated.

The last same OB's installed on a light application were factory delivered with 10 pitch props that were found over propped, installed a 9 pitch prop and the hole shot was much faster than with a 10.

Happy Boating

 

[Guest]

A 4 stroke with power tilt and electric start is going to be way too heavy for that little Whaler, even if you found one.
Back in the day, many yacht owners put 25 OMC 2 strokes on those boats with great success and they flew, but those engines only weighed about 115 lbs. 4 stokes are weight hogs, they're slower, and its doubtful you can even find a 20 hp 4 stroke short shaft (15") with power trim, just be prepared for excess weight and low stern freeboard if you do.