70el77 johnson

[Lsxfbody]

Hi guys im new here, i regularly viewed topics when researching my current boat. I have a 1977 14.5' Peterborough tri-hull with a 70hp johnson on it. I have had the boat for just over a year, pulled the fron two seats out and built a casting platform with 3/4" marine plywood fiberglassed bothaides and then fiberglassed into the entire front it is about 3'x4' if memory serves me correct. I installed 60mm vinyl to the top and the door as i made the complete underside a storage for extra gear and saftey equipment when i replaced the foam and floor. When i pulled the floor up it was not wet but i changed the foam anyways while i was there and inspected the stringers for moisture. I had a few issues last season that kept me off the water for most of the season, steering cables jammed up, engine issues, tilt motor died. Spent $1700 getting everything fixed inculding a new top end, waterpump and impeller, along with a bunxh of ignition issues i thought were carb issues, i also rebuilt the controls installed a tach and new throttle cables. I never had a tach last year but it would top out at 35mph with a omc ss prop 13x?? The last number is rubbed off so unsure of what it was, engine only ran like it was a 40hp last season. Engine has 121-119-120 compression and on the dyno it has no more hesitation under load and revs up to 6000wot, just curious if anyone has a similar set and what prop they use? I have a 13x19 ss that im going to test out in a few weeks now that i have a tach and make a guess from there on changes i need just curious if anyone has a similar setup so i know what top speed and prop size i can expect?

 

[Lsxfbody]

Oh i forgot to add it turns starboard under acceleration, from what i have read it can be corrected with trim tabs(i only have tilt) is there anything smaller than the ones that mount on hull id rather have something mounted onto the outboard. My outboard came with a "happy troller" mounted to it but i have a 55lb minn kota so the trolling plate will be comming off

 

[David Young]

My 1977 Evinrude 70hp on a MFG 15'3" tri hull does 35mph at 5500rpm. I messed up the unknown factory prop and replaced it with a 13.250 X 17. My tach messed up because of a bad rectifier when put the new prop , it was showing 5,000 rpm at full throttle. I replaced the rectifier but haven't had a chance to take the boat out this year yet. I believe a 15 to 17 pitch prop is the normal pitch for our hp and boat size. I'm no expert

 

[Lsxfbody]

Ya thats about the size i was getting from reading aswell just wanted to hear what others where running and at what speed/rpm. Im ordering a 13x17 turning point ss today pa1pa2-1317 is the model number. I wont be back from work up in fort mac until the 30th so hopefully the new prop will be in by the time im back and i can get some test done. Very nice boat in your signature btw! Mine still needs some new paint and 2 more new seats for the back but that will probably be a winter project cant waste precious time on the water lol

 

[jimmbo]

I know which boat you have, there were oodles of them around here in the late 70s. Being a light load for the 70, it might have been propped with a 19 in prop. But with all the extra weight you've added a 17 would probably be your best choice. The turning starboard upon acceleration is probably from the motor being trimmed too far in. I assume you do not have power trim? Try moving the tilt/trim pin into a hole further from the transom

Speed range with a 17, 27 - 33 mph; with a 19, 30 - 37 mph based on 4500 - 5500 rpm @ 10% slip

Your working in Ft Mac? That place looks like a war zone in some spots. Here in the capital I've seen a lot of people who are in the evacuation centers

 

[Lsxfbody]

Ya im north about 80km up at cnrl but when we fly over she looked pretty bad, i qas thinking a 17 would be perfect for fishing and still being able to tube, have the 19 as a spare for if i just wanna cruise. I will try tilting it back one hole i have it in the second away from the transom right now. It o ly startes to turn like that once i put the brand new steering cables in i think the old packed in grease was holding it before because it was a 2 handed turn when i firat got the boat and now i can full turn with my pinky lol

 

[David Young]

Ya thats about the size i was getting from reading aswell just wanted to hear what others where running and at what speed/rpm. Im ordering a 13x17 turning point ss today pa1pa2-1317 is the model number. I wont be back from work up in fort mac until the 30th so hopefully the new prop will be in by the time im back and i can get some test done. Very nice boat in your signature btw! Mine still needs some new paint and 2 more new seats for the back but that will probably be a winter project cant waste precious time on the water lol

Thank you for saying my boat looks nice. Come back and let us know how the props work. We're having cool weather for the next several days so i can't take the boat out to see if my tach is working right or not. Good Luck.