Originally Posted by 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. update: This "improved performance" claim is in my experience very misleading! yes, top speed may theoretically be improved because a 20 will be stern heavy with a bracket, making it easier to get the bow up to reduce wetted surface and friction drag. However this is only useful if you plan to only run in flat water inland rivers and lakes! On the other hand, if you plan to actually use your seacraft's rough water capability and and set the boat up for comfortable operation on plane in seas of 3'+ (meaning your min planing speed should be down around 12 mph like it originally was on all the moesly designs with 300 lb motors!), my experience is that once you add "fixes" necessary to offset the negative effects of an aft cg shift, you may find that you've actually reduced performance! After i installed the bracket with the new 427 lb motor, min planing speed was about 22-23 mph, which is totally unacceptable because a relatively light 20 will be airborne at that speed in 3' seas! After i installed the right 4b prop and a fin on the av plate to get more stern lift, my wot speed had dropped from almost 50 mph to 39 mph, although the boat would then hang on plane down to 12 mph, with a dramatic improvement in rough water ride. By contrast, a good friend of mine recently repowered his 20' seafari with the same motor but mounted it on the transom . . . It pegged his 50 mph spedo on his very first run, but it still planes at low speed! Bottom line: A bracket on a 20 may actually hurt performance unless you can move enough gear (console, gas tank, batteries) far enough forward to offset the cg change created by shifting a heavy motor aft by 2-2.5'!
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 427 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
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12-19-2021, 05:56 PM
Thanks... Thinking of Redoing my '73 Seafari
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