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Hi, just picked up a '77 Whaler Harpoon 5.2. My question is: what is the max weight/h.p. motor I can use?
My mechanic doesn't think a 2.5 would be adequate (just for on/off mooring and unforeseen circumstances). Would a Minnkota 55 lb. thrust be too little? 5 or 6 h.p. seems overkill with weight and h.p.

Thanks for suggestions.

Larry
 

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Sounds like your mechanic might be trying to upsell you to something you don't need. 2.5 horsepower would be loads of power for a Harpoon 5.2.

55 pound trolling motor would also work but the battery is a pain and you would get better range from a small gas motor.
 

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I found the owners manual online. Can't link pdf's so just google harpoon 5.2 owners manual.

Maximum horsepower listed is 4 horsepower.
 

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Had one of these. Used a 4 hp 2 stroke which were US legal at the time. Problem is weight destroys trim so go for the lightest engine you can find. I sailed the boat in Mass Bay. Prevailings are southwesterlies so returning was dead into the wind and if there was traffic it was safer to motor than sail. If you’re in a similar situation get the most light weight high HP you can.
 

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Here's a little article that explains how to calculate outboard horsepower requirements for small sailboats.

The article recommends 1 hp/550 pounds displacement.

A harpoon 5.2~565 pounds. So, 1.5 hp should theoretically be about right. Except, I don't know of any quality modern 1.5s. 2.5 hp is the closest hp rating that I know of and will provide plenty of excess power for pounding into a chop (I don't usually run my 2.3 on my 900 pound boat at full throttle into a headwind/chop because the slamming gets excessive).

https://improvesailing.com/guides/how-to-calculate-outboard-motor-size-for-sailboats

Note, when the Harpoon owners manual was written in the 70s 2 stroke outboards were the norm and weighed in around 35-40 pounds.

Most modern 2.5-4 hp outboards are 4 strokes (the old 2 strokes were terrible for the environment). A modern 4 stroke 2.5 weighs about the same as a 1970s/80s 2 stroke 4 hp. A modern 4 stroke 4 hp weighs about %50 more than their old 2 stroke counter parts. Excess weight on a dinghy is not a desirable thing. Excess weight at the extreme ends (transom) of a dinghy is even worse and will increase the boats tendency to slam when powering into a chop. A new 4hp outboard also costs nearly double what a new 2.5 costs.

Adding extra hp to a sailboat boat with a 15 ft waterline is not likely to result in a dramatic increase in speed even with a head wind. 4 knots is about all you are going to get.
 
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