More on hp ratings!!!

[alumistar]

Back to my question that even started my trek through this wonderful site...What would be the highest hp I could put on a 12ft Starcraft manufactured in April 1972. USCG does not require BIA plates on anything made before <br />Oct,31 1972. How lucky could I be? Except, I am rebuilding the transom right now due to rotted wood. I wonder if the transom has been replaced before,'cause there is no BIA on the old wood anyway, the boat has three seats, 9 cross members and one keel plate. If the keel plate is an issue, I have no problem fabricating a couple to go on either side...what to do, what to do?

 

[sloopy]

Re: More on hp ratings!!!

That does not mean you can put a 90hp engine on there. SO your not that lucky.

 

[alumistar]

Re: More on hp ratings!!!

ummm, yeah dude, didn't quite mean that BIG. ya know? kinda curious about what's safe but effective for my big butt.

 

[JB]

Re: More on hp ratings!!!

Howdy, Alumistar.<br /><br />Sounds like a boat that would do well with a 25HP.<br /><br />The USCG website has a formula for homebuilders to calculate safe hp. I would check there.<br /><br />SLOOPY: Chill, Dude. The man's asking for advice, not rebuke (look that up in your Funk and Wagnalls. )<br /><br />Good luck.

 

[MurdockJr]

Re: More on hp ratings!!!

alumister I have a 68 12ft sears with three bench seats and it is only rated for 7.5hp.

 

[cobra 3.0]

Re: More on hp ratings!!!

If all you have is a 12ft aluminum fishing boat, 7 1/2 hp is about right. 9.9hp would be as much as I would care to try. My buddies had rented a 9.9 hp for their 12 ft boat years ago. It worked fine. A 15 hp would be dangerous.

 

[Solittle]

Re: More on hp ratings!!!

I would be comfortable with a 9.9 or 15hp. I have a 9.9 on a 12'er. A 25 would be too much for me.

 

[Mark42]

Re: More on hp ratings!!!

My brother-in-law has a 25hp on a 12ft john boat. When it's wound up, all that is in the water is the prop.<br /><br />Don't do it like that. Too scary.<br /><br />Plus the NJ state police stopped us for speeding. We didn't get tickets because we had the right fishing license.<br /><br />Have fun!

 

[sloopy]

Re: More on hp ratings!!!

My 12 foot aluminum boat is rated for a maximum of 15 Hp. An eleven foot PWC can have 90hp and be under powered....

 

[walleyehed]

Re: More on hp ratings!!!

Interesting Sloop........never looked at it that way, although the PWC setup is simular to that of an F-16....thrust on the center-line kinda deal....Hummmmmmmmmm......

 

[walleyehed]

Re: More on hp ratings!!!

alumistar, maybe we've talked before-seems like I just told someone I had a 12ft Starcraft rated for 15hp, but had a Johnny 10 on it.<br />Your description of your boat is identicle to mine, and I feel 25hp would be too much, and I am somewhat of a performance nut. I operate at 3500ft and the 10hp does well, although 15hp at my elevation would be better. That being said, I feel your boat would perform real well with a good 15hp. Good luck! <br />BTW, if I had a dime for every trip I made across Grand Lake and up to chicken hill, and maybe threw in a penny or so for every trout I caught in front of Lake Cove Marine, where I worked, I'd be rich I tell ya!!!!

 

[JasonJ]

Re: More on hp ratings!!!

Can't really compare a 12 foot aluminum boat to a PWC. PWCs weigh a lot more that a 12 footer, and the hull bottom is designed for high speeds and stable handling. A 12 footer is very light, and the hull design isn't much to write home about. I always see 9.9s on those things, but thats just what I see. You couldn't pay me to own one of those things, not enough boat around me....

 

[flashback]

Re: More on hp ratings!!!

I have a 3 point hydroplane with 18 hp. boat does about 60mph. fast enough for a boat eight and half feet long..

 

[alumistar]

Re: More on hp ratings!!!

how 'bout I do the 15hp then? I mean, I am at 8500ft. or so, and I weigh in at 280. with the altitude effectively dropping my hp on a 15 to around 9-11hp. that would be an alright deal yeah? should I maybe do a little transom work for the added torque? 15's are about 70lbs in the two-stroke class, so I'm not worried about weight.

 

[Jdeagro]

Re: More on hp ratings!!!

Alumistar;<br /><br />It sounds like you are concerned about the HP because of the weight in the boat, and ability to plane. In many cases the difference between a 9.9 and a 15 HP is all in the wide open throttle. The low end torq which is needed to get the boat up to speed and on plane may be the same.<br /><br />Once you deside and have a good idea of the loads you will have in the boat, I would be happy to give you more advise if I can.

 

[envy83]

Re: More on hp ratings!!!

I'm definitely suprised to see JB on the higher side of the crowd, but I'll definitely agree with him. Depending on the setup of the boat (namely v and beam) a 12 foot could be great with a 25 or a 15. The biggest difference is going to be weight. Look the weights up on www.NADA.com and then hang that much over the transom. In a boat that size, that's what is going to make the difference. You're rebuilding the transom so you can make it incredibly tough, and you can always back off on the throttle, but how the boat balances is tougher to change.

 

[alumistar]

Re: More on hp ratings!!!

nautijohn, <br />i'm thinking that if i go with a 15hp, than i can get a couple things accomplished; first, would bring me up to 9hp or higher, obviously due to altitude choking. second, possibility of running a console, putting me in the middle of the boat and evening out the weight distribution. my final concern before ending the chaotic rampage in my head and doing the 15 thing is; should i be overly concerned about the transom or stern area or sides or floor buckling. cause i tell you what, these lakes here might be small, but if you go down you'll be a hundred yards down current before you come back up for air! kinda sucks, but that's where the rainbow trout live, and dang they are some good eating!

 

[JB]

Re: More on hp ratings!!!

Well, it was stupid of me to mention 25HP.<br /><br />Seems everyone stopped reading when they saw that.<br /><br />GO TO THE US COAST GUARD SITE AND FIND OUT HOW TO DETERMINE SAFE HP FOR YOUR BOAT!!<br /><br />Maybe that will get through this time.

 

[alumistar]

Re: More on hp ratings!!!

jb, if my calculations are correct and i do have a soft chime with console steering, i can do a fifteen, no problem....thanks for the help. i downloaded the 53 page documentation on boat building and the next evolutionary challenge might be to build my own?????hmmmmm....i wonder.......how fun could that possibly be.....wish i knew more about fibreglass......maybe my larson would be more than an anchor by now.....thinking,thinking,thinking......

 

[Jdeagro]

Re: More on hp ratings!!!

Alumistar;<br /><br />I don't think a 15 hp is a problem under your conditions, and if you check the weight differential between the 9.9 and the 15 you may find that there is none. As for the construction of the boat, you are better able to determine if the hull is sound or not. <br /><br />As for performance, I say again check the specs on the motor because a 9.9 is often the same as a 15 except for higher RPMs. This means that the low end performance would be no different. A quick check would be the std. recommended prop. If the 15 has a larger prop or one with more pitch, the low end torq may be better. This would be a good reason to move up. I had an older Nissan 9.9 two stroke and the only difference between it and a 15 is the carb linkage. The fifteen is allowed to open the throttle more. Prop size and all other specs are the same. Therefor there is no difference in performance until I am at the higher RPMs.<br /><br />In other brands the 15 is a completely different motor. Check the specs.