Four Stroke vs Two Stroke power and Black Brant III

R

Ryan B

Member
So I have been reading lots lately and finally ordered plans for a BBIII. It seems like there are conflicting reports on power requirements on these boats and I am wondering out loud if it may be partially related to age/type of motors involved? I am probably going to buy a new motor for this boat and it seems like there is a big jump in weight/cost from the 20hp portable category (usually the same block as a 15hp) to the 25 hp four strokes out now. I have been looking at the short shaft Tohatsu 20hp and it seems like a good fit for the boat. I do not want to spend lots of money on a new motor and find out the boat will not plane off with it. It seems like a new four stroke with the right prop should push a couple guys, dog, guns, decoys etc...a reasonable planed off speed? I have read that the way motors hp numbers are calculated now is at the prop instead of the powerhead-can anyone confirm this?
 
Erik, 20 HP is too small for the BB3. Go bigger or you will be disappointed. There are mixed reviews on the performance with a 25, you might be OK with just yourself. 30 hp is a good choice. Stick with a 2 stroke if you can just for the weight savings.
 
Erik, 20 HP is too small for the BB3. Go bigger or you will be disappointed. There are mixed reviews on the performance with a 25, you might be OK with just yourself. 30 hp is a good choice. Stick with a 2 stroke if you can just for the weight savings.
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Pete nailed it. I run a 15 its to small.
 
Erik,

I agree with Pete too. I powered mine originally with a 2 stroke 25 hp mercury, it seemed a little underpowered. I believe Devlin was hanging 2 stroke 30 hp originally, I found a '98 40 hp mercury (same motor different reed) I've been running it for 6 years. It seems just about right.
 
Its always been at the prop for an outboard, measured in ft-lbs of thrust with a tank rig that the motor was mounted on.

Due to the weight increases of the 4 strokes Devlin reduced the HP rating to 25hp. the HP rating is based on motor weight as well as hull shape, and the extra 20 to 30 pounds (or more) for a 4 stroke required the max HP rating to drop.

You will have to study the prop recommendations for your motor and get one that will meet your performance requirements.

I run a 25HP 2 stroke and the factory prop worked well with only me, but not with two men and a dog. I found for my hunt conditions I needed to run a SS prop, which I was not able to find in the same configuration as the factory prop. My SS prop does not produce the top end racing speed, but with two men and a dog it pushes fine.

Sadley, the swamp has such low water now that I can't run an outboard and have switched to a small long tail putt putt putt putt putt

A 20hp on a BBIII with a hunting load will not "plane out" I would guess. If both guys weigh less than 150lbs it might.
 
I built a BBIII last summer/fall, when it came time to buy the motor I asked about the same question here and based on the advice given I bought a Yahama 4 stroke 40 hp. I hunted the ocean and bays on both sides of Cape Cod all winter and it is a great fit. Pull start, 1st pull every time any weather. Barely hear the motor at idle, power when you need it and sips gasoline.
 
Erik,I have a 25 Merc on mine and for 2 guys and gear its a load,I went to a 4-blade after-market prop made a big differance,like Pete said a 30 is way better,Brian
 
Erik, Todd C is selling a new 25hp yamaha short shaft over on the clasifides for $2800.00 Well worth taking a look at. Tom.
 
Thanks for all the input. I just got the plans in tonight and will be picking up plywood this week to get started. I guess I will start keeping an eye out for 25-30hp motors.
 
Had to pile on to this post...I built a BBIII last year and mounted an older 30hp two stroke with factory prop. It runs like the wind when I'm alone, does just fine with a second hunter and gear, but can barely get onto plane with a third hunter. I built the BBIII because of its flexible utility value. If you plan on hunting alone or with one additional hunter I would recommend the 30hp. Anything else and there will be times you wish you did.

Have Fun!!

KT
 
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