need tips for speed/efficiency

Samantha

Cadet
Joined
Oct 8, 2008
Messages
8
Hi! I'm new here and I could use some help understanding small boats and motors.

I recently bought a 10' flat-bottomed aluminum "john" boat and 4.5hp motor on Craigslist. It's pretty fun, but I'd really love to get it to plane.

My motor currently hangs down low into the water and seems to create needless drag. I'm thinking that if I build a plywood deal that reinforces the aft wall (or whatever it's called) I can also increase the height so that the prop sits just below the bottom of the boat. Would this increase speed/efficiency?

I also noticed that the motor adjusts for angle. It is currently set to be as far down as as it can be. Should I adjust it? What does this affect?

Thanks!

Sam
 

marine4003

Lieutenant Junior Grade
Joined
Feb 3, 2008
Messages
1,119
Re: need tips for speed/efficiency

Sam..Its doubtful you will get more speed out of that motor,as for planing, does the motor hang perfectly vertical to the rear (transom) or offset, having the motor tucked back "under" the transom will help keep the bow down, IMHO going to a 15hp will solve alot of your problems , and ..No, building a jack plate for that small of an engine wont help ...you need more HP.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: need tips for speed/efficiency

It is possible to plane with a 5 hp.Your 4.5 and your flat bottom is an ideal candidate.
You need a tiller(steering handle) extension,so you can sit in the middle seat.
Raising your motor may help a little especially if you get it close to planing speed.We had a 12' steel flat bottom it planed easily with a Gale 5 and a 180
pounder in the middle seat.I mean it "popped" on plane.
Back part of boat is the Transom.You can raise the motor a little by adding 1/4" sticks to the top of the transom just be sure the clamps have a good grip
and it pumps water.Sticks are just to hold the height as you tighten the clamps.After establishing the height use a single piece of wood.My Merc 500 50hp sits on about a 1" stick.
 

Samantha

Cadet
Joined
Oct 8, 2008
Messages
8
Re: need tips for speed/efficiency

Thanks for responding, guys!

Marine4003-

I love the size of my boat; it fits perfectly on my car and in my apartment(!). Somewhere along the way I was told that the maximum legal HP on my boat was 3! Well, it came with this old 4.5, and it sure doesn't seem dangerously fast. I can kinda see how having the motor tucked farther under would help, but it's as far as it will go.

Steelespike-

The fastest I was able to go was definitely when I was alone in the boat and in the middle, and a steering handle definitely occurred to me, though the controls for my motor are these sliding switches, and not on the handle :(. Still, I'll try something.

What do you mean yours "popped" on a plane, that it would get up on one intermittently?

Thanks for the idea of using sticks. Not sure why that didn't occur to me. But don't you think that at the very least, having less shaft to cause drag between the bottom of the boat and the prop could only help? If so, I may need to raise my motor a lot.

Is there some diagram of dos and don'ts for outboard motor efficiency?

Thanks again guys!
 

rrhodes

Chief Petty Officer
Joined
Jun 24, 2008
Messages
636
Re: need tips for speed/efficiency

Pictures would help out so we can see how your motor sits on there now.
 

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: need tips for speed/efficiency

I have a 14 ft. with a 5 hp and she planes. Runs 13 MPH with me alone. You'll get there. There is a horizontal plate on the motor just above the propeller. Where is that in relation to the bottom? Also, try all of the trim angle settings, you may be burying the bow for all we know . . . ;)
 

junior1113

Senior Chief Petty Officer
Joined
Jan 29, 2009
Messages
763
Re: need tips for speed/efficiency

keep raising the motor untill u hear it pull air then go down a little that will solve drag ussue. pop on a plane they mean jumpun a plane quickly your probobly not going to get this thing on a wave jumping chine walking plane but should be able to cruise around at a good speed buddies got a 12' aluminum w 57' evinrude 5.5 cruises good with 2 people .the old motors have a longer shaft then most newer jon motors so we had to move it up 1 1/2" to get all we could off of it
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: need tips for speed/efficiency

Yes the less motor in the water the better. You might be able to build up the transom in such a way that you can use it like a jack plate.making it easy to get more height and fine tune to a fraction of an inch.By using the stick method you can get an idea how far you can go before redoing the transom.
 
Top