20' SF with 1996 Johnson 115 V-4 (enough power?)

StrangeBrew · #1 05-12-2008, 04:55 PM

All,

I just purchased a 1996 Johnson 115 for my 20' Potter Built. Do you feel that the 115 HP is enough power? I was looking for a 150 HP, but came across a deal on the 115 that I could not pass on. Thanks.

Fr. Frank · #2 05-12-2008, 05:02 PM

The 115 will be fine. You should get mid 30's, and cruise in mid 20's. Many new 20' SeaCrafts were rigged with 85 hp and 115 hp outboards. My 20' Seafari was rigged new with an 85hp OMC, and I recently repowered from 150 down to 90 hp and am well pleased.

StrangeBrew · #3 05-12-2008, 05:10 PM

Thanks for the reply. Do you think i will require trim tabs to help it out of the hole?

Bushwacker · #4 05-12-2008, 08:44 PM

Fr. Frank is right - the 20' hull is very efficient and does not need lot's of power to be a very nice riding boat. I ran a 1975 115 V-4 (90 hp at prop!) for 31 years on my Seafari and never had any complaints or durability problems. 115 hp at the prop would be even better! Ran it fairly hard with a very heavy load, cruising at ~4500 rpm/20kts on 6 crossings to the Abacos, a trip of about 165 nm, averaging about 2.8 nmpg. (The 140 I/O Seafari's averaged about 5 mpg on this same trip!) These boats were designed in the mid-60's for motors of that size, so they're very well balanced with them (not stern-heavy, so they'll ride well and plane at 12-13 mph!). I bought the boat & motor before the V-6's came out, so I used to actually hope the seas would kick up a bit so the guys with V-6's would have to slow down so I could keep up with them! The 20' Seafari can generally keep up with most 23-24' non-SeaCraft boats in 2-3' seas; the SeaCraft 21 is another story, however! I could never keep up with that boat if he did not also want to cruise at about 20 kts; same with the 23 to a lesser extent. Would highly recommend trim tabs, even on a 20 with a light motor - they'll make your boat think it's about 3' longer!

StrangeBrew · #5 05-14-2008, 01:19 PM

Thank you for the info! The next question becomes prop size and pitch...Everything I've read leads me to 13 1/2" with 15 degrees of pitch...Does that sound about right? I know I'll have to test it, but want to start off close. Thanks.

Bushwacker · #6 05-15-2008, 12:44 AM

My 90 HP "115" would turn a 13 3/4" diameter x 15" pitch SST prop to about 5600 with light load and 5300-5400 with heavy load and top raised. Was able to raise motor 1" and picked up about 3 mph relative to aluminum prop of same size. Your motor should be stronger than that so might be able to handle a little more pitch or diameter, but I'd start with that, and stay with aluminum or composite till you get it dialed in for the load you normally run. Better to over rev than under rev!