What is the appropriate Hp for a given weight?

[jusdecul]

I am about to buy a Princecraft DLX BT fishing boat that weighs 480 pounds. The Max Hp rating for the boat is 40. Unfortunately, I only have enough money to buy a Yam 25 4-stroke. With it I thought I could power the boat and it was still low Hp enough to use as a trolling motor (I heard 4-strokes would rev low enough) The dealer tells me that he only recommends the 40 or not much lower. Does anyone know what the rule of thumb is for weight vs. Hp and speed (if that becomes the only issue)? Would 25 hp move that boat or get it to plane?

 

[roscoe]

Re: What is the appropriate Hp for a given weight?

The 25 will plane your boat and you....But you will be very disappointed in the performance, when you then add a friend or two, fill the livewell, batteries, fuel, extra fuel tackleboxes, cooler.<br /><br />Personally, if this is your budget limit, then I would make the move to a 2-stroke 40 with power tilt and trim, for the same price, or less.<br /><br />You can backtroll, add a trolling plate, or use a drift sock to slow you down if needed.

 

[ledgefinder]

Re: What is the appropriate Hp for a given weight?

One empirical formula is<br /><br />((horsepower/weight)**0.5) * 200 = mph<br /><br />If you can't read that it's divide horsepower by weight, take the square-root of that quantity, then multiply result by 200. The weight's in pounds, and the multiplier factor is 180 for deep v-hulls, 220 for flat-bottom boats like jon boats, and 200 for 'average' hulls. <br /><br />If you're boat weighs 480, and using 400 for motor, one passenger & gear, I get 33 mph.<br /><br />The formula's from a Whaler fan website (www.continuouswave.com), and I find it's usually a little high, that is optimistic about the speed you'll attain. Does give you a reasonable way of comparing the effect of 25 versus 40 hp.

 

[Jack Shellac]

Re: What is the appropriate Hp for a given weight?

Welcome to the site, PCET. I too think you'd be much happier with a motor bigger than a 25 0n this boat. Have you considered a late model used motor? Look on iboats to see what they're running. The upside of a 25 is that they're usually easy to sell when you get ready to move up.

 

[billy-bobby]

Re: What is the appropriate Hp for a given weight?

I had a 16 ft Princecraft open utility (Starfish) which was wide and deep, and about 300 lbs. This is your DLX BT stripped down. I tried a 25hp 2stoke on it one time and it worked okay, but I was much happier when I purchased a 35 hp 2-stroker. I couldn't afford a 4 stroke at the time, and was conscious of the weight/hp thing. I would recomend going no less than 35 on your boat, and four-stroke if you can afford. You would be unhappy going as low as 25hp.

 

[jusdecul]

Re: What is the appropriate Hp for a given weight?

Thanks all for your comments. It's a lot easier to take that kind of advice from users than from a salesman. Would anyone know if trolling becomes out of the question with a 30-35 4-stroke. I'm used to trolling at low speeds with a Johnson 6. That thing putts me along so slow, sometimes I feel I'm not moving. Then the walley hits... Ahhh walley... I'd like to avoid having 2 engines on the back (weight... gas tanks... control...) I know I could add one of those plates behind the prop, but I'm curious as to how slow a 4-stroke can actually go.