CONTINUOUSWAVE

I'm re-powering a 1976 SPORT 15 with a F70. Should I add a [Springfield Marine "Transom TUFF'NER"] or plate of some sort?

Also, in what bolt hole [should the engine be mounted] to optimize performance?

I don't have a particularly strong opinion about the value of adding a Springfield Marine Transom TUFF'NER. I suppose the value of adding one would be in inverse proportion to the general condition of the transom on the 1976 SPORT. If the transom were in excellent condition and retains its original strength, I don't know that use of a Springfield Marine Transom TUFF'NER would be required.

What is the weight of the engine you plan to use in the re-power?

Engine mounting height is described in terms of the height above the lowest position, measured in units of 0.75-inch or "holes." The usual engine mounting height for starting performance evaluation is to begin at one-hole-up mounting. Then, with experimentation, try higher engine mounting heights until the desired performance is obtained. Exactly which engine mounting height works best depends on many factors and is principally affected by the propeller being used.

Describing "which hole" is not useful as it leads to ambiguous descriptions. Please read the pinned article at the top of this forum:

Engine Mounting Height
viewtopic.php?f=7&t=739

First of all, congratulations on the choice of motor. You won't regret that decision.

The F70 weighs approximately 40 pounds more than the 70 HP 2 strokes of the mid 70's (257 vs 220). Unless you have reason to believe that your transom has weakened over the years, I see no reason to be concerned.

My F70 is mounted approximately 1- 1/2" above the lowest position (2 holes up) on my 15 footer and I am very satisfied with the performance. I must qualify, however, that mine is "stern heavy" as I have added a rear fishing deck and poling platform.

Hope this helps.

Great info! Engine goes on Tuesday and I'm very excited to put new life in this boat.

The [transom] is strong. It has minimal cracking for a 40 year old boat. I was just thinking the transom saver could be a good thing. I bought a generic version not the [Springfield Marine Transom TUFF'NER] because I don't like the branding

Still open to suggestions to use it or not. If you don't use a tuffener, is there input on best hardware (i.e. Washers) to use? Also additional input on height is appreciated.

Thanks!

The F70 on my Supersport 15 is mounted two holes up - that is, one hole below the highest mounting position. It is quite likely the tech at the dealer will want to mount it lower - do not let him/her do so.

After lengthy experimentation, the prop I like best is the PowerTech SCD3 in a 16 pitch. If you are located where you can run flat out and top speed matters to you, you may prefer a 17 or even an 18 pitch.