Motor for 12ft aluminum

[fishcracker]

I have a small Johnson 4hp for the boat. The max size rated is a 9.9. What in your guy's opinion would be the best size motor for this boat??<br />I can get a Mercury 7hp for $500...completly serviced. Would that be a good choice??

 

[ferrariman]

Re: Motor for 12ft aluminum

i have a thirteen foot aluminum with an evinrude 7.5 and with me and a buddy in the boat it goes just fine. And if the motor is as good as it sounds, its a deal.

 

[tashasdaddy]

Re: Motor for 12ft aluminum

agree

 

[Paul Moir]

Re: Motor for 12ft aluminum

Mount a second 4hp and you'll go twice the speed of stink. <br /><br />Seriously though, find out the year of the 7hp (7.5hp?) Older mercs used driveshaft material that rusted badly in salt water; they are very rare around here. You might ask the condition of the current driveshaft when the water pump was serviced. You really want to know about the water pump because it proves that you can still actually remove the lower unit.

 

[cobra 3.0]

Re: Motor for 12ft aluminum

I had a 7.5 Merc. It was a great engine except when 3 people were in the boat. Then it was a dog. A 9.9 would be a much better choice.

 

[Boatist]

Re: Motor for 12ft aluminum

Get a 9.9 at least. Even with a 9.9 boat likely will not plane with 3 adults. MY 14 foot will not plane with a 15 HP with 3 adults.

 

[fishcracker]

Re: Motor for 12ft aluminum

Alright what exactly is planing. (noob) I'm guessin me 4hp won't plane.

 

[waterinthefuel]

Re: Motor for 12ft aluminum

That's when the boat gets up on top the water. You know how when you accelerate, the nose typically comes up, then as speed increases comes back down again? That's when its said to be "on plane", like a skier over the water.

 

[Boatist]

Re: Motor for 12ft aluminum

As you start moving the boat will push water with the bow. The water will push out to the sides and move around the boat. At this point your hull is a displacement hull.<br /><br />As you increase speed the bow wave will cause the front of the boat to raise up on the wave. As you add even more power the bow will rise so high it starts over the bow wave. More power and speed and the bow wave goes farther back on the boat until the stern is actually raised the bow has come down any your riding the wave almost like a Surfer. When you get on top of this wave your speed will increase alot with the same power. At this point the boat is on plane. Your fuel useage will go down even with your Higher speed. The speed to get on plane is different for every boat but in general somewhere around 18 MPH. More speed at the same power so you fuel mileage has gone UP. <br /><br />When you slow back down the stern will go down first then the bow.

 

[fishcracker]

Re: Motor for 12ft aluminum

You think a 7HP merc will get the 12 ft'r on plane??

 

[STeveZ]

Re: Motor for 12ft aluminum

Lets see, I can offer these examples from experience, all are aluminum vee-hulls.<br /><br />16' + 18hp - flew, a great combo<br />14' + 9.9 hp (twice) - serviceable but too slow for me, wouldn't plane<br />12' + 15 hp - fast, a little overpowered maybe<br />16' + 20hp - too fast, engine too heavy<br /><br />My guess is that a 12' + 7.5hp combo would fall into the "serviceable but too slow category", especially w/ passenger(s). I would prefer a 9.9

 

[studlymandingo]

Re: Motor for 12ft aluminum

To get on plane, you will need a planing hull, not a displacement hull. You would want to determine the type of hull you have before you decide whether the motor will allow you to plane.

 

[bryantjb3]

Re: Motor for 12ft aluminum

How wide and deep is this 12 footer? Flatbottom jonboat? If so a 9.9 would be a bit much.

 

[Pogo123]

Re: Motor for 12ft aluminum

I just sold (and miss is already) an Alumacraft 12 ft semi-v that I pushed with a Suzuki 6HP (71 pounds). With just me (+tank, battery troller, tackle box, cooler, etc) it made 19 1/2 knots (by GPS) on the Intracoastal. With 2 guys it made 15 Knots.<br /><br />I then installed the carburetor off a Suzuki 8 (bigger inlet throat, but same mounting) and picked up 4 to 5 kts, with a noticable increase in acceleration ... but that wee skiff was also a pretty slippery hull.<br /><br />Your setup (bottom line) sounds just about right.<br />And you, depending on your hull design, should get about the same results.

 

[fishcracker]

Re: Motor for 12ft aluminum

M boat is flat on the bottom but tapers up in a V shape towards the bow...see pics below. The only pics I have right now.<br /><br />

<br /><br />

 

[Boatist]

Re: Motor for 12ft aluminum

I never seen a 12 foot aluminum that was not a planning hull. Your is a planning hull. Very little dead rise on the stern so would be rough rideing in any chop while on plane. I would look for the 9.9 HP since that is your max rating. The 15 HP Johnson on Evinrude is the same weight and same block as the 9.9 but has a different carBuretor and exhaust. I think your rig would plane with two light adults but not with 3 adults.

 

[tashasdaddy]

Re: Motor for 12ft aluminum

good boat, for the 9.9, anything bigger it would get squirrely and be a waste of power. put a long hose on your gas tank, and if you want to fish alone put the tank in the bow. it will help a lot. it looks like it only has a 3/4 plywood transom, with 3/4 on the outside. you may want to beef up the inside with another layer of 1/2 or 3/4.

 

[deejaycee_2000]

Re: Motor for 12ft aluminum

15hp will be purrrrfect .....

 

[cobra 3.0]

Re: Motor for 12ft aluminum

I run my '97 15 Evinrude on a light 12ft fiberglass. It flies and planes easy with three people on board. I have no idea what the boat is rated for...most likely a 9.9. <br /><br />If you use common sense and adjust your speed for the water conditions, a 15 would work fine too. However, I'd stick with the hp rating for your boat.

 

[fishcracker]

Re: Motor for 12ft aluminum

Alright a 9.9 it is. Now to find one for a bargain.