Outboard Brackets, Pro's & Con's

[Bushwacker]

This question comes up often enough that I thought I’d start a new thread, as I had the same questions many of you are probably having. If you’re wondering, after having gone thru this learning experience, would I do it again, the answer is ABSOLUTELY! However, here are a few things you need to think about before you dive into what will no doubt be a more expensive project than just a transom rebuild! Don Herman, PaulB, Snookerd, Briguy, and Captains Chuck & Lloyd, feel free to chime in on anything I’ve missed or otherwise screwed up! (These comments apply to the 20' hull; for a 23, the pro's are the same, but the con's are probably less severe, as the bigger boat should be a little less weight sensitive, although I'd still be careful about running real heavy twins.)

PRO’S
1. The biggest advantage of the closed transom/bracket set up is the safety aspect of keeping water out of the boat from a big breaking following sea. Unless you’ve been in that situation, it’s probably hard to put a value on it, but it’s a very big deal to me!
2. It's really nice for diving and it provides more room in the boat since you can eliminate the splashwell. You've essentially increased boat length by whatever the bracket setback dimension is.
3. It also keeps noise and smoke out of the boat, if you’re still running an old carbureted 2-stroke.
4. Improved Performance. Most before & after tests have shown that a bracket adds 2-3 mph in top speed because motor is running in cleaner water, allowing you raise the motor relative to bottom of boat. A similar increase may occur in optimum cruise speed.
5. Improved on-plane trim capability. Maybe it’s just the 25” shaft motor, but an aft shift of the motor increases the lever arm for both weight and thrust loads! Power trim definitely has more effect on running angle than I had with a 20” motor mounted on the transom.

CON’S
1. Downsides are it changes the boat balance because you've shifted the weight of the motor aft, which moves the boat CG aft, and tends to hurt ride and increase min planing speed. On the 20' hull, the Seafari is less stern heavy than the cc models, so it's a better candidate for a bracket IMHO.
2. Low speed maneuverability will be slightly affected, because you've also shifted the boat's pivot point aft. In my own case, I found that the new Seastar hydraulic steering system had a shorter stroke than my old Hyanautic/home-made rig, so it doesn’t turn the motor all the way to the stops, which exaggerated the maneuverability problem. As near as I can tell, all the factory made hydraulic systems have the same stroke, and I haven’t figured out a fix to that yet.
3. You'll have to move the axle on your trailer back a couple feet to keep enough weight on the tongue.
4. All brackets I know of are made for a 25" shaft motor, which might be an issue if you're not repowering or having a bracket custom made. The higher that powerhead is from the water, the better!

A few key things you need to pay attention to if you add a bracket:

1. Motor weight! Because of the CG issue, lighter is better! I would not consider the 450-500 lb 150 4S Yamaha, Honda & 150/175 Zuke, and the big block V-6 200+ hp 2 strokes because they're so heavy. That leaves the 140 & smaller Zukes, the Merc Optimax, the small block V-4 & V-6 E-Tecs among the new motors, and the earlier small block V-6 2 strokes. If you run offshore a lot, LESS (power & weight) is MORE. The light 20' hull will start to go airborne at about 20 kts in seas over about 3', so you don't need a big motor for that type of operation. I considered the 375 lb V-4 E-Tec rated at 115 hp (really about 120-125) but they weren't in production yet when I bought mine. I’m obviously not a speed demon, but the 150 (really 165) E-Tec at 429 lbs is overkill on power (will run almost 50 mph in flat water) and is the heaviest motor I'd consider. That said, it IS nice to be able to cruise at 4000 rpm/30-35 mph AND carry on a normal conversation! (It’s quieter than the 4-strokes at that speed.) It’s also nice to be able to outrun a thunderstorm if you screw up and get surprised by one!

2. Look for a bracket with the biggest flotation tank you can find, either a Hermco or an Armstrong designed for twins (but use a single on it). Reason is to maintain some self-bailing capability. My rig is still self-bailing, but just barely; I leave the scupper plugs in and depend on the bilge pump if I leave it in the water overnight.

3. Try to run the smallest setback you can with the motor you’re using. I could get away with 18”, so 30” on the Hermco is overkill, although nice for diving! (Don – how hard would it be to offer your bracket with various setback dimensions?) Making a custom bracket like Strick & Big Shrimpin did is a good idea if you have those kind of skills!

4. You will probably want to run trim tabs, a 4-blade stern lifting prop and maybe a Doelfin or equivalent to maintain good low speed (12-13 mph) planing capability for rough water operation. The flotation tank doesn’t help when you’re on plane, so all this stuff helps compensate for the weight shift.

5. If you already have hydraulic steering, all you need is new hoses, throttle and shift cables that are about 6' longer, at least if you rig them like Don Herman recommends, where everything runs down into the bracket and then thru the transom inside the flotation tank to keep a nice clean transom. If you have cable steering, you'll want to switch to hydraulic steering, which I'd recommend even if you don't go with a bracket.

These are just some thoughts based on my own experience. A lot of folks are probably trying to make this decision, so you other guys with brackets, feel free to chime in! Denny

[Snookerd]

Well done Denny! The biggest floatation area, ie - Hermco Type will yield the best results.

[Bigshrimpin]

Great summary!! That covers everything.

Just want to mention that the low speed maneuverability is a big issue for me. Raising the motor 2 holes helped some with the reverse maneuverability issue(not sure why). The swim platform also makes a great tool bench.



24" would have been the shortest set back for me to get full tilt with the motor.

[McGillicuddy]

Hey Big, Curious,can Merc shafts be extended on I-6 and 2.0L models? Can 20" shafts go to 25"?

[Bigshrimpin]

I'm pretty sure bayMFG makes a kit for the inline 6's.

The 2.0L v6's use the same baymfg kit as the 2.4L and 2.5L. Also for the 2.0L v6 you can also find the 5" spacer, 25" shift shaft, cut your own 1/2" copper tube, and swap in a 25" lower with the long studs(just make sure it's 2:1 ratio lower).

[ROBCAR]

Great info Denny! This get me closer to what I need to know before making a decision on my 20ft MA. Since I am redoing my transom, this is the time to make a drastic change....bracket, no-bracket and just raise the transom to 25", but would have to replace the o/b anyway (currently a 200hp Mercury with 20" shaft)., trims and hydraulic steering.....it may have been cheaper to buy a brand new 2008 SeaCraft ... javascript:void(0)

[strick]

Everything Denny said is right on. In summary if you go with a bracket on a 20 cc make sure you:

1. Get as light weight a motor you can.
2. Get a bracket with as large a flotation chamber as you can
3. Keep the weight as centered in the boat as you can (fuel tank, batteries etc...)
4. Go with the minimum set back that will allow the motor to tilt up.
5, Get trim tabs (however I hardly ever have use mine)

If you go about it right then you wont be disappointed in the way the boat handles. Just ask Bigshrimpin how nice the boat in the pic below handles. And backing up is not all that bad.

LIFE IS GOOD




strick

[Bushwacker]

Great looking rig Strick! Have to admit that motor (130 Yamaha 2-stroke?) looks to be just about the perfect weight and power match for the 20' hull! Denny

[CaptLloyd]

Great summary Denny!

It's great to see all the issues presented at one time, instead of broken up into several different threads. Thanks for putting it all together!! BTW, I'm with you, if starting over again, I would definitely go with a bracket! The 23' WA will eventually get a bracket.

I would add one thing, make sure the bracket matches the transom angle, otherwise, the platform will not be level.

And to reiterate, watch motor weight. My 427 lbs Suzuki 140 4 stroke is has heavy as you want to go on a bracketed 20'cc.

Lloyd

[Snookerd]

Strick-That is an amazing boat. You really nailed down all the requirements with the addition of your well made floatation bracket for top notch performance.