Will my boat be underpowered?

[ultra353]

I picked up a new project boat and wondering if it will underpowered , it's a alumacraft pro 17 aluminum bass style boat. 17'5 long and 73" beam powered by a '85 Mercury 50 hp. The hull is rated for 75 hp. My current boat is a smokercraft 151 resorter powered by a '89 Mercury 40 hp, tops out about 28 mph. If performance is close i would be ok with it. I would really like to put a Evinrude/johnson 70hp from late 80's early 90's on it.
What are your opinions on the current setup and how much of an improvement will I gain with 20 more ponies, thanks

 

[Teamster]

I'm sure it would be okay with the 50,.......

But more fun with a 75,...............

How much do yous want to spend????

 

[ultra353]

Well, I'm selling the smokercraft in the spring, figure I'd sell the 50 hp that's on it now and I have a few other motors that I'm flipping , I will have enough for the 70 hp and refurbish the alumacraft. It's kinda of a hobby of mine to buy these boats and motors and flip 'em

 

[rallyart]

You're not likely to complain about having more power.

 

[Bob_VT]

Just something to consider.......... Yes you will get much better performance with a larger motor........ and more fuel consumption.

Now if you are looking for speed....... (I am a Starcraft SS 16 owner) I would suggest a fiberglass hull. I have tested this myself and if you read the performance reports from the various manufacturers you will see the aluminum hulls are the slower ones.

Go with a newer motor, one that parts are available for and have fun!!

 

[bonz_d]

I have a Classic 16 which I'm running a 1983 Johnson 60hp 2 cylinder. These 2 boats should be appx. the same overall weight. The 60hp performs just fine even with 2 adults and 2 larger children. The Classic 16 is also rated @ 75hp and call me chicken but I would be very nervous with one and actually think that is overpowered. The 60hp also saves me almost 50 lbs overall in load capacity.

 

[pckeen]

The boat's a little underpowered now - you'll do better with the 70, and gas consumption may not increase as much as you would expect - with a larger motor, it won't have to work as hard....

 

[gm280]

I have a unique thinking about buy things like this. You can always throttle back some, but you can't make it go faster unless you have the capability. In other words, more power is better then underpowered. I use to fly and teach R/C flying. And I can tell you the bigger the engine the better to make things work. Same with 4 wheelers too. You can throttle back and cruse but when you want to go faster, you have to have the HP there... But that is just my opinion...

 

[steelespike]

Fiberglass faster is a good point.Over the hearts reading various tests many times a comparable glass may be faster even though usually heavier.
If healthy your 50 will probably run about 30 mph,a healthy 70 probably about 35.I think you will notice the difference more as you add weight.
As someone said the 70 will be loafing at the 50s top speed.
Speaking very roughly a 50 will use about 6 gallons per hour at wot. the 70 about 8 gph.

 

[ultra353]

Thanks for all the great answers ! Since the motor is an '85 it's rated at powerhead not the prop. ( been reading that here on the forum)So, it's really only a 45 hp on it, is what I'm thinking. Isn't the rule of thumb you want 80% of the rated hp to get decent performance? I thought I read that on here. 75 max hp x 80% = 60 hp. That's why I was asking about the performance.
I'm not a speed freak but if I take my kids out with all the gear and/ or pull them on a tube it would be nice to have the extra power if needed.

 

[Watermann]

That era of Johnny/rude 3 cyl 70's are great motors and one would be a perfect motor for that size of boat. Good fuel economy and plenty of power. I think it's a very good choice.

 

[pckeen]

Rule of thumb is you don't want to power a boat with anything less than a motor that is 70% of the max rated hp, otherwise you can have real performance problems.