May seem like a dumb qustion to some, but...

[MAXXIE]

May be a dumb question, but I'd like to know. The HP rating on any given boat, mine is 85 hp, what is that basically referring to? The weight the transom, the stress the motor put's on the structure of the boat, both, or what? I only ask because my O/B is a 1985 & it's quite heavy. With the new O/B's out there, are they any lighter? I was just thinking that if the HP rating is based on the weight hung on the transom, could I buy a new, higher HP motor that weighed the same? Please spare me the "You can only go with the rating", the "Why would you want", or the "It's not save or legal" comments. I know all of that. I'm just asking the question. TANX, MAXX

 

[JB]

Re: May seem like a dumb qustion to some, but...

Many factors, including the weight of the outboard, structural rigidity of the hull, design of the hull and where the boat is piloted from (tiller or console?), but not limited to those, are considered in determining the safe maximum HP on a boat. Boat length, width, depth and transom height also matter.

In general, I think new outboards weigh more than their ancestors. DFI 2 strokes and all 4 strokes are the heaviest.

Old carbed 2 stroke outboards are high in HP per pound, but they have no ECUs or complex injector systems to make them cleaner, quieter and more economical.

 

[LongLine]

Re: May seem like a dumb qustion to some, but...

I'm no expert but I'd believe the whole rating thing has to do with maintaining the structural integrety of the transom during stressful situations. The really stressful parts being the hole shot; ie quick acceleration, plowing into a wave, throwing it into reverse, hitting a log and trailering the boat ie bouncing around. If it was purely weight then those fishermen (albeit the dumb ones) wouldn't sit on their motors. (They'd be swimming)

Tom B.
(LongLine)

 

[Joe Reeves]

Re: May seem like a dumb qustion to some, but...

Maxxie Quote: "May be a dumb question, but I'd like to know. The HP rating on any given boat, mine is 85 hp, what is that basically referring to?"

Various horsepower engines are in the same weight class... a few pounds here or there. Main concern is horsepower/propeller torque.

Maximum rated hp = 85hp....... Install a 140hp in same weight class....... Look forward to transom damage!

 

[Silvertip]

Re: May seem like a dumb qustion to some, but...

This topic is discussed over and over again, always with the idea that because my engine is old the new ones with way more power would be ok to install. The net result is there is formula that the boat manufacturers use to calculate the maximum HP a boat can safely handle and engine weight is not a major factor since there are many engines with the same HP with vary different weights. To make this perfectly clear, why do you think a manufacturer has identical hulls, but one has tiller steer and the other has side console steering, yet they rate maximum HP differently (lower on the tiller). It is called SAFETY. A tiller steer boat is very twitchy compared with a helm steer -- hence the lower HP rating. The hull design, depth, length, and width are key values. Some small sport boats handle like sports cars and are actually designed for a high HP engine yet a fishing boat of the same length would be dangerous with the same HP. So the long and short of this is that the HP rating is there for a reason and it doesn't matter whether it is 40 year ago HP or last years HP. DO NOT overpower a boat unless you own nothing of value. Any incident whatsoever may cost you dearly when the courts are done with you -- whether the incident was your fault or not. And lying to your insurance company about the overpower may leave you high a dry (or with empty pockets) as well.

 

[jay_merrill]

Re: May seem like a dumb qustion to some, but...

This may help. Start at page 5.


http://files.dnr.state.mn.us/education_safety/safety/boatwater/backyardboatbuilders.pdf