Outboard Brackets, Pro's & Con's

[Bertram87]

Thanks Bushwacker, yeah that was what I was thinking was a dedicated line out of the main hull. The T was just an idea without too much thought into it.

[23Seacraft79]

bushwacker, did you do the single or twin hermco bracket? if so, what engine/shaft length did you go with??

[Bushwacker]

Originally Posted by 23Seacraft79

bushwacker, did you do the single or twin hermco bracket? if so, what engine/shaft length did you go with??

I used a single bracket. I believe the twin bracket is only applicable for the 23 or a boat with an 8' beam, so don't think it was intended for a 20 with a 7.5' beam. I have a 25" motor but, as explained below, I've now raised it a total of 5 3/8" above where it was originally mounted, so a 20" E-TEC would probably work, although it would have to be mounted in next to the lowest hole with the powerhead 5" closer to the water. Might be different for a Suzuki which runs a very large prop that just barely clears the AV plate, so a Zuke might have to run deeper. (These comments only apply to a 20' hull; I have no clue about the bigger bracket on a 23!) For best performance on most motors and props, you generally want the Anti-Ventilation plate just above solid water when you're up on plane, although some props can run higher than others depending on the design. Don Herman mounted my bracket right where you want it, i.e., as low as possible for maximum flotation, and the swim platform height is perfect, about 2" above the water, but almost awash when a couple of guys get on the platform.

However my AV plate was totally buried even with motor raised as high as it would go, so Don redrilled the motor mount holes to raise motor another inch to the very top of the mount pad; can't raise it much higher because lower bolts would be right in plane of the swim platform. AV plate was still buried at 3.25" above keel (1st 3 pics below), so I added a Vance Mfg. JPL4300 manual jackplate which had the smallest setback of any I could find.

I raised motor with jackplate to where the AV plate is now about 6 1/8" above keel and AV plate is finally above water! (last 2 pics) I picked up about 100-150 rpm, which let me turn a better prop (heavily cupped 4B SS BRP Cyclone 14.5" x 15p ) up to 5450 rpm with max load (optimum is 5300-5500 rpm for my specific model motor). That prop change raised WOT speed about 3 mph and increased cruise mpg by 0.2-0.5 mpg! My previous PowerTech 15x15 4B SS prop will spin 100-150 rpm faster but acts like it has less pitch than the Cyclone, evidently due to cupping differences, since both have the same blade area as determined by comparing circumference of blades. Both props run fine at the highest location, with no tendency to ventilate during sudden hard turns, although I can't/don't have to trim out as far as I did with motor mounted lower settings. I do see some effects of the extra 3" of setback of the jackplate because boat has an annoying tendency to porpoise, so I'm currently investigating some schemes that will allow same motor height but with minimal setback.

One thing I've concluded from all this is that the Trade Factor of raising motor 1" for each foot of setback, often mentioned on the internet, is TOTALLY BOGUS, at least for my setup! In my case, the Trade Factor works out to be: 6.125" increased motor height/(33" setback/12") = 2.23" height increase/foot of setback, or more than 2X the commonly quoted number!

[tommyg29]

Adding to this old thread with my (new to me) 89 Seacraft. I spent a long time looking for the right boat, and this one fit all my needs, including the platform bracket. I believe its an Armstrong, and not quite as wide as I would like, but on my sea trial it seemed to work great! Hopped up on a plane almost immediately, and performed and maneuvered better than I expected. Dont have any details for now, but at least a couple pictures.

[Bushwacker]

Nice looking rig; as a Tracker model it's a bit longer which will help it balance a little easier. I would guess that it's a bit stern heavy unless PO moved batteries/console/gas tank forward. What sort of min planing speed will it hold? The original Moesly designs with 300 lb motors on transom would plane at about 12 mph!

[tommyg29]

Im going to put it through some tests on sunday. It has a 200hp 2 stroke on it, so almost 500 lbs there, but the batteries are up in the front under the console, and it has a 107 gallon fuel tank, so I imagine that pushed the CG a little forward, however, I think most of the "extra" tank sits aft of where the standard tanks sat, so, maybe not. Regardless it jumps out quick. I will definitely check at what minimum speed and conditions it keeps on plane and report back, and I have the hydraulic steering also, so will check maneuvering too.
Thanks

[Old'sCool]

Very nice and should fly with the 200. I would properly fix the empty transom screws ASAP.

[Bushwacker]

Hey Tommy - didn't notice that it was an HPDI motor . . . thought it was a 4S, but you're right, I guess they're almost as heavy! But it'll have much more mid-range torque than a 4S, so should be a strong running rig. If it has trouble hanging on plane at low speed, you might think about adding an SE Sport fin on the AV plate (no drilling req'd), and/or a stern lifting 4B prop. Those 2 changes totally changed the planing characteristics of my rig, for the better!

Man that's a huge gas tank for a 20! I hope it's got plenty baffles in it! Otherwise, that much gas sloshing around in a partially full tank might cause some really weird handling sensations! Regarding hydraulic steering, I was amazed to discover that the modern Sea Star systems only provide about 60% of full rotation that motor is capable of! Before adding the bracket, I had a motor on transom with a home made Hynautic system I designed myself with enough travel to put the motor on the stops. I added the bracket and Sea Star system at same time, and it took me a while to realize that the substantial increase in my low turning circle was due to the steering system and not the "longer boat" effect of the bracket!

[tommyg29]

Originally Posted by Old'sCool

Very nice and should fly with the 200. I would properly fix the empty transom screws ASAP.

What screws you talking about?

[tommyg29]

Couple pictures showing how it sits. A little low in the back but not much water comes in. The shot of the stern while trolling was with me and my son standing back there.
The Sea star steering turned about 5 full turns lock to lock, but it sure seemed to need constant correction at WOT, which is about 44mph at 5400 rpm. I kept trimming and playing with the trim tabs looking for the sweet spot and it almost seemed like I kept cranking the wheel to one side to keep er on course dead ahead. My first experience with hydraulic steering and its different feeling from direct mechanical linkage.