More HP for little boat

[Squeakit]

I have a 12ft Landau jonboat, originally rated for a 6hp motor, but have reinforced the transom (to take a little more weight) and want to stick a bigger engine on it for a little more speed. I am presently using a 5.5hp Evinrude or a 7hp Sears/Eska to push the boat; performance for either of these engines is pretty much identical - 16mph GPS with just me in the boat. (The old 'rude is a couple of tenths faster than the Eska) I'm going to look at a used 15hp Evinrude and am wondering what kind of speed increase to expect, other factors being equal? Is there a formula for speed vs. horsepower? Would appreciate any comments. Thanks.

 

[JB]

Re: More HP for little boat

Yo, Squeakit.<br /><br />Hp ratings of boats take into account much more than the transom's weight carrying ability.<br /><br />In the case of your Jon, it is probably not intended to go any faster than 16mph due to the overall structure ability to take pounding, etc.<br /><br />I think a 15 on that boat would be dangerous. Even a 9.9 would be taking unnecessary risk.<br /><br />If you must have more speed, first get a boat built for it.<br /><br />Good luck.

 

[Squeakit]

Re: More HP for little boat

Thanks for the reply, JB. Boat is extremely light, narrow, shallow draft with pointed bow and flat bottom. Zips along nicely at 15-16mph but forget it if the lake is choppy from wind or boat wakes. Seems very stable for such a small boat, but it is little more than an aluminum shell and most of the boats I have seen with bigger motors were much heavier and more solidly built. Your point is very well taken - thought maybe I'd avoid WOT except when water is very smooth. Have to see this 15 and size/weight very important. Trying to make a low-budget little hot-rod but don't want to do anything too stupid either <G>

 

[envy83]

Re: More HP for little boat

Your not going crazy with a 15, but if you do do it, make sure you have Solidly reinforced everywhere you can and if the motor has a "kill switch" lanyard, wear it!!! I've thrown myself from an almost identical set-up (at a GPS of about 31mph) and did not enjoy the boat continuing to chase me while I swam to shore.

 

[JB]

Re: More HP for little boat

Envy, he is talking about overpowering the design by 150%. That is a BAD, BAD idea. <br /><br />We need to offer responsible advice here, not invitations to death defying stunts.

 

[dakotashooter2]

Re: More HP for little boat

My brother had a similar setup. If you do it be carefull. It was fine as long as he went in a straight line. As soon as he started to turn it got pretty squirly.

 

[The Marine Doctor]

Re: More HP for little boat

Unless you want to get your boat recertified. Stick with what it is rated for.<br /><br />There are ratings for a reason.<br /><br />TMD

 

[Squeakit]

Re: More HP for little boat

Hey guys: Thanks for your input. I definitely don't want to wind up in the water with my boat chasing me <G> I did go and look at a 15 and it seemed a little bit heavy - the guy at the shop that had the motor said it might make the boat too stern heavy. I'm definitely in no big rush to do this if it's going to be seriously unsafe. Was also thinking about an 8hp as it is lighter and less radical in the power department, but since the 5.5 and the 7 seem to produce about the same speed, it doesn't seem like an 8 would do much. The boat has a bimini top on it and later this fall when it isn't so hot, I will use the boat without the top and probably pick up a little speed from less wind resistance. Just a toy boat and a personal challenge- would like to at least break 20. 25 would be GREAT. 31 would probably leave a brown trail in the water (mine)

 

[Chinewalker]

Re: More HP for little boat

Hi Squeakit,<br /> FYI, the Eska is hardly considered a "strong" 7hp. Not sure how they rated them, but I've never seen an Eska keep up with a similarly rated Johnrude or Merc. I would guess that if you were to run a "real" 7-8hp motor, you'd see quite a difference...<br />- Scott

 

[envy83]

Re: More HP for little boat

JB is right. That is not a safe set-up and I'm lucky to have been okay after trying it. On that small a boat and motor, you should be able to get<br />a similar boat that is wider and with a V-hull that would better handle a 15 hp for very little investment (I've found boats like that in the classifieds for around $100).

 

[Squeakit]

Re: More HP for little boat

Hi Scott: Funny you should mention. I was wondering that myself. My old 5.5 Fisherman actually seems a little bit faster than the Eska - only a couple or 3 tenths, but figured it was a higher quality engine and also a 2 cyl. Both engines are in excellent tune. Was wondering about a newer Merc 8hp - wish I could try one out without having to buy it first! 

 

[Squeakit]

Re: More HP for little boat

envy83: You are absolutely right - getting a beefier boat would be the obvious solution. Unfortunately my wife and I are emotionally attached to this dumb little boat and don't want to part with it. This is sick, I know, but I just want Lil Squeak (the boat) to Be All It Can Be <LOL> and so I'm going to have to make some concessions for safety with an eye for more power. I really appreciate all the good advice!

 

[SeaHorse]

Re: More HP for little boat

Your boat should go this fast:<br />8 hp = 19.3 mph<br />9.9 hp = 21.4 mph<br />15 hp = 26.3 mph<br />25 hp = 34 mph<br />I have a 10 foot boat that is “suggested” to have 5 to 7.5 hp (doesn’t have a stinkin “capacity” plate) The 10 hp I had on it wasn’t up to planing 2 people easily so I reinforced the transom and put my old Johnson 25 with a 17” pitch 2 bladed prop on it and it really flies. Out in the big lake (400+ sq miles) it gets rough when the huge cruisers and Cigarettes go by and the low end pulling power comes in handy to pull her up the waves instead of bogging down. <br />Jon boats aren’t made for this kind of stuff so I’m sure you’ll keep that in mind

 

[Columbia]

Re: More HP for little boat

If you exceed your 'rated' hp, you will be in violation of Coast Guard regulations. If you are ever checked by any official patrol folks you won't be happy. Additionally, a Jon boat with a narrow bottom is, IMHO, a poor candidate for a larger motor due to instability athwartships and pounding potential.

 

[Squeakit]

Re: More HP for little boat

Thanks for the reply Seahorse. You just told me exactly what I wanted to know. If I'm going to plunk out any more money for a larger engine, I'll go for the 15 as it weighs the same as the 9.9 and has the potential, poTENtial, mind you to go like bejesus if I should be so foolish as to open it up with just me in the boat. I won't. My little 15ft Bayliner goes 27mph and I don't see my little toy going that fast. However with me and my wife and a full picnic basket plus folding camp chairs and fuel going up Topock Gorge against the current, it would be nice to have the option of reserve power and it would be foolish to have a motor that weighs the same and goes alot slower. Weight is my prime consideration at this point as well as price. New 15's are too **** expensive, but if I can get a screaming deal on a used one and it isn't too heavy I just might go for it. Would really like to be able to put one on the boat and try it out (very carefully) but unfortunately this is not always possible. I'm also aware of the CG regs and appreciate the Caution Flag old sailor. I'm definitely in no rush, as my old 'rude runs like a watch and I always have the old Eska to back it up. But I'm a-lookin' LOL!

 

[Solittle]

Re: More HP for little boat

For the sake of your family make sure that your life insurance is paid up and your will is up to date. They may need it.

 

[Squeakit]

Re: More HP for little boat

Just got ahold of a used 15hp Evinrude which I will try out on the lake tomorrow very, very, carefully. Got it from a local OMC boat wrench who is letting me give it a try before I decide to buy. Figure I can't lose with this proposition and I plan to take me and my wife and my GPS and one 3gal fuel tank. Plan on opening throttle VERY slowly and NOT doing WOT unless it feels very secure and probably not even then. Model #and serial# sticker is illegible, but a sticker on the pull starter says TST1559 and has a date of 11-07-1996. Does this sound like a model #? Does anyone know if '96 15hp Evinrudes have any particular weak spots? Will post results from this experiment tomorrow - at least I'll know if this is a great idea or not so great <G>

 

[93bronco]

Re: More HP for little boat

mite be a good idea to leave wife so she can collect if something happens.<br />just an idea.

 

[Just Jed]

Re: More HP for little boat

Emotionally attached? If you get a lid fitted for it you can use it for a permanent vessel if you know what I mean. Stick to the rated H.P. It is rated for a reason.

 

[Link]

Re: More HP for little boat

Been following this since the first post.<br />Lets hope we hear from him tomorrow (saturday)<br />You can lead a horse to water...