Evinrude E-tec 75hp or 90hp

[sturra82]

Just a quick question for the boaties out there, I am looking at putting a new motor on my 14ft fibreglass runabout, is rated at 75hp from back in the 1970's but has no weight restriction that i can find. Both the 75hp and 90hp are the same weight so just wondering if i can go the 90hp to give me a bit more power to pull a skier if i have to. Thanks.

[PAR]

What is the width of your transom, not counting rub rails, just the hull? If it's about 5' 4" (1.62 m), then 75 HP is right. A 90 HP engine would usually want a transom about 6' 5" (1.95 m).

The next thing you'll want to look at is the thickness and general condition of the transom core. A nearly have a century old transom is a thing to worry about, if increasing the power you're hanging on it. A 75 HP transom will usually have a 1.5" (38 mm) core, but a 90 HP will usually have a 1.75" (44 mm) or 2" (51 mm) core.

Food for thought . . .

[Mr Efficiency]

That's a big jump. 5''4 to 6'5 ??? What is the make of the boat Sturra82 ?

[sturra82]

Its a Cruisecraft Rogue 14.
The other reason I thought about the bigger motor would be that I obviously wouldn't have to push the bigger motor to do the same speed as the 75hp and with the weight being the same I couldn't see the problem but I will definitely measure the transom as suggested. Thanks for the info.

[whitepointer23]

hello sturra. i just looked up the rogue in jeff websters 2nd hand trailer boats book. they were rated for up to 85 hp, that would have been a v4 johnson which is heavy , same as 115 and 140 . a 90 etec will be no problem. just make sure the transom is still solid, cruise craft are well built but it probably had accessories screwed to it over the years allowing water into the ply. it has a 1.83 mt beam.

[Mr Efficiency]

90 horses would be too much for one of those old girls. The hull is only a moderate vee and I'd say the old 70 johnnos that weighed about 100 kilos were enough weight and power. There were plenty getting round with 50/55 hp. It is not a performance hull, just an honest plugger. And they are getting quite long in the tooth, it would be prudent to examine the transom and underfloor area for signs of rot before splurging on a new motor. Even if in good condition, the hull isn't worth much, certainly not enough to justify an expensive new engine, IMO. Unless it is a family pet !

[whitepointer23]

i reckon the 90 would perform good. the good thing about it is it an outboard, he can update the hull later and he will already have the engine to go on it. i have driven 1 with a 70 johnson and it was a bit doughy.

[Mr Efficiency]

320 pounds for a 90 e-tec, thats heavier than any 85 horse engine from the era.....and now they are prop rated. And a lot to spend on an old hull, if it was a Haines 146 I would say go for it, but that was a beamier, deeper vee about 20degrees, and much better able to use that power. I would say the Rogue would be about 15 or 16 degrees and more suited to quieter waters, and 90 hp will make for difficulty with insurance.

[Mr Efficiency]

I'd say if the transom is shot, it is basically the end of the road. That is the way I would look at it, it would be hard to justify spending substantial money to restore it, then fork out big $ with a new engine. Doesn't make economic sense, unless sentiment trumps the resale value issue.

[whitepointer23]

you make good points, but etec is only 8 lbs heavier than an 85 v4. i like the rogue, not as soft as the haines but better to fish out of. i would look at a tldi tohatsu if it was me. i have heard scary things about etecs. don't know if the storys are true though.

[PAR]

90 HP divided by 14' is about 6' 4" worth of transom, 75 HP divided by 14' is about 5' 4" of transom beam. It's a fairly crude formula, but does get you in the ball park.

You need to do a lot more then just support the 90 HP as a static load. I'll bet the nearly half a century transom core, stringers, etc. aren't up to the various tasks, either in thickness nor condition.

[gonzo]

The weight of the outboard in relation to the HP is not the most important parameter. A higher HP will make the boat go faster increasing the slamming and other dynamic loads. Even though the boat may float on her lines when static, at speed she may break up.

[Mr Efficiency]

It was a mass production boat in the 70's built about half an hours drive away from me, seen plenty of them on the water and the vast majority were 70hp or less. The fact they were happy with 50hp tells you 90 is overkill.

[whitepointer23]

85 was the factory max rating.

[Mr Efficiency]

The 85 johnrude was a cross flow v4 of 1300-odd cc capacity in the 70's,( I think the last of them was 1632cc in 1980, becoming a 90 thereafter). The Mercury 85 was a 4 cylinder straight 4 with somewhat less cubic capacity. If it was designed to accomodate those engines, they were not as strong as a 90 e-tec, prop rated. Spending that money on an old Rogue---forget it !