How to pick an outboard with enough HP, etc.???

[MarkTakacs]

My father in law has a 16' center console (not a popular brand) that we have crabbed on for years. It had a 50hp Force engine on it that ran flawlessly for years......now it is trash (another story).

This motor never seemed to have enough power for this boat to me...to get up on plane quickly especially with a chop. It has a semi tri-hull design....if that makes sense.....definatelty not a v-hull. My father inlaw tried to blame it on the prop???? Then one day while crabbing at Rocky Point the identical boat pulls up with a 75hp motor. (I WIN....at least in my book)

The coast guard/manufacturer decal calls for a maximum HP of 115HP.

My questions are what would be a minimum HP outboard motor for this boat based on my description and the maximum HP sticker?

How can you determine the best motor for this boat?....is it the maximum HP recomendation?

If a person is outboard mech. is selling a reconditioned motor with the top cover re-painted and new decals.....how can you tell what the HP rating is?

Thank God my buddy has a good boat

Mark
[grin]

[WildeOne]

50 HP was clearly too small for the boat. You can't go wrong with a motor close to the max HP the boat is rated for. You don't use the HP all the time, but it's sure nice to have when you do. I am repowering my boat and going with the max the boat is rated for, since the existing motors (85% of rated HP) didn't always cut it. The other advantage of bigger is you will normally run the motors at lower RPM (and correspondingly lower combustion temps) than smaller motors running hard most of the time.
Jim

[OUTCAST1]

75% of max rated is what I consider adequate. 50 HP you had before was definitely underpowered. 85%-90% is more than enough for most purposes. 100% is for special heavy duty uses, multiple water skiers, towing water toys, other boats, fishing with fat women, etc. Seriously, I would not hang 100% of rated power on an old boat. The transom typically deteriorates with age and structural integrity is just not what it was when new. If the boat was rated for 115HP when new, 90HP is a reasonable size. Good luck, stay safe.

[Bob H.]

A 70hp to 80hp should be fine for a 16cc. You don't want to hang too much weight on the back. You may have had the wrong prop on the 50hp, poor weight distribution, or too much weight preventing you from getting on plane.

[rj]

The Above advice is right on at least 75% of max rated HP

If you are not sure about the HP or year of a reconditioned motor

get the model # and the serial # from both the Engine block and the external serial # plate..you can then lookup the year & HP online or go to a local dealer for that brand and ask them to look it up

be sure and get the #'s from both places,,it is quite a common practice for rebuilders to assemble motors from many different year motor parts

[Capt.Nick]

Like everyone else said not enough power.Min.2/3 max.rated but a little more is better..Now about the prop.For best performance,the rpm's tell it all.The engine should run at the "WOT" wide open throttle top end of the rpm recemended by the manufacturer with your regular expected normal load..That's somewhere around 5k or more.Any less and it puts a strain on the engine parts,much more and it's reving too high.The heavier the load..the less the pitch you should have and the wider the diameter should be.A well cupped prop will also pull a heavier load better.Pitch means that 1 revolution"theoretically" would move the boat say 17in.but that theory is only hypethetical.It is based upon a screw moving through solid wood.Water is formless and alot of slip occurs.Figure out how fast you would be moving'theroetically" if your boat was turning 5k rpm.with a 17in.prop.If you can,call the manufacturer of the boat to get a ball park idea of what size & pitch should be used.if not,some books will give an idea based upon length by wt.

[OUTCAST1]

When doing above calculations, better figure in the reduction of motor drive train, usually about 2:1. Otherwise, the above numbers will have you wondering why you aren't going 75-80 mph!