Bracket modification

[flyingfrizzle]

Originally Posted by Bushwacker

Friz,

Not sure of the dimensions of your bracket, but your swim platform looks much higher than mine, and the motor mount surface also looks like it's taller than mine so I suspect you could lower the bracket quite a bit from where it is in that last picture, and you'd still be able to raise the motor high enough.
Denny

At the time I took the picture I had the bracket just sitting up against the boat. I plan on mounting it a bit lower than where it is pictured. If it works out right the tub will be about 3" up from the boat keel. If you look closely at the bottom of the bracket flange you can see where I notched it to match the steps on the bottom of the hull so that I could get it close a possible for maximum flotation. After reading everyone's post on mounting these brackets I made mine higher so to avoid the bottom motor bolts from landing where the swim platform will be. I also made the mounting lip much higher so I would have enough to raise it to the proper height. Doing it this way will make the platform not as close to the water as I would like but I don't dive so it is not a big deal. The main thing I wanted was maximum flotation and a motor with the av plate out of the water while on plane. I plan on using the boat to pull the kids on tubes and such and will add a ladder if needed so they can get in and out more easily. Thanks to all who have posted an this topic, it has help tremendous in making the bracket and now installing it as well. If all my measurements work out the way I planned, I should be able to mount the tub about 3" up from the keel and still be able to set the motor at +4.5" above the keel and still have a inch or so to go up more if necessary. I haven't drilled no holes yet but this weekend I plan on raising the boat high enough to get the motor under her and mocking everything up and seeing where I stand. I hope to keep the tub as low as possible but will raise it up to get the motor height right if I have to.

Thanks again for the help everyone and I will post how it turns out once it is bolted on!

[flyingfrizzle]

I finally set the bracket last night. Got it as low as possible for maximum flotation. The tub ended up 3" above the boat keel and the motor mount was about 29" from the boat bottom. I think I should Be able to get the motor up 4"-5" no problem. The swim platform is not as low as I would like it but it had to be higher like this to allow for the lower motor mount bolts to hit below the platform to get the required height. Looks good on the boat. I will be using flat bar to back the bolts on the inside and also changing the current bolts to ss carriage bolts to give a nice rounded head that will be seen on the lower flange due to the reverse direction of it. The flange will need a half circle cut out in the bottom to allow the drain hole to be accessed as well. Now that the dry fit is done I will make some small changes and get it prepped for a final install.

















Here is a picture of how it looks not that it is painted:

[fredbrad]

The height of 29" of the top mount bracket worked for you ?, I would like to know since I have mounted one in a 23cc and I am at that same height of 29", I am still in time to cut an inch for fear that it is high the engine and can not lower it a little more

[flyingfrizzle]

Originally Posted by fredbrad

The height of 29" of the top mount bracket worked for you ?, I would like to know since I have mounted one in a 23cc and I am at that same height of 29", I am still in time to cut an inch for fear that it is high the engine and can not lower it a little more

Yours may be different than mine. The length of all 25" legs on different brand outboards are not all the same per manufacture. The best way to check it is to mount the outboard if possible, then use an stright edge down the hull bottom sticking out past the transom, measure up to the AV plate and then set the motor height to where you want it. Most need to be 3.5-4.5" above the stright edge. The main measurement you want to worry about is the height that the AV plate is from the bottom of the hull when the outboard is trimmed so that the AV plate is parallel to the hull bottom. I have found for 22-24” setback you want to be around 4” up from the hull bottom. A non-bracket hull on the transom can handle the AV plate up around 1-1.5 inches. Rule of thumb for brackets is to add 2” up from the hull bottom for each foot of setback on the bracket.

The mounting height actually worked out fairly well once I got the weight sorted out. There is only 22” of setback but the distance wouldn’t change much for a 24”bracket. I would say this height is more of a maximum performance and low drag. All around ride and going after zero slippage you may be able to go an inch lower but the AV plate would start to get back down in water and drag or spray slightly.

I originally I thought it could still go up a inch or so but I had too much weight in the rear. You can see the hull sitting low in the rear on some of the earlier pics on the build thread. (The pic below is after the weight adjustment)
The heavy rear was mainly due to:
1) The bracket weight was too heavy as the Dusky drives are very over built
2) I had two 60-70lb batteries under the rear two seats in the boat
3) The 200hp Mercury is only 400lbs but still heavier than design of 300lbs
4) I never added a full size tank and the 12 gallons of fuel is in the hull was in the rear of the fuel cavity.

The boat would porpoise if trimmed up in clean water and start chine walking when over 60 mph when the weight was in the rear. It was not balanced out well. This boat really made me a believer in weight distribution in these 20 sc hulls. Not that I didn't before but I really seen the difference a few hundred pounds made moved forward.
I ended up taking two 100lb batteries from our UPS system that were swapped out for new and reused them mounting them one each in the forward storage compartments on each side. I moved the temporary 12 gal fuel tank forward in the fuel hatch area and blocked it where it wouldn't slide back under power. (Still need to get my 60 gallon tank mounted) Once the 160lbs was removed from the rear and 200lbs was added up front it was a completely different boat. I can trim the motor where the AV plate is fully out of the white water and the boat dose not porpoise any longer, No chine walking, the bow dose not rise as bad hitting wakes, it turns much better without rolling as bad, the boat is more stable under way, way more stable at rest, the water line is even down the hull sides, she is not bow proud any longer, holds plane at a lower speed, best of all she rides like a dream now.
I was thinking of adding trim tabs but after adjusting the weight I really don’t need them. Tabs are always nice but there is no need inshore where I normally run. I would likely add tabs if I was to keep her and was to do a little more offshore with the boat but will be building another 20 with a different custom lay out sometime in the future. The hull defiantly has more power than needed but I often don't have time to fish and find myself going out at 6pm for an hour or two at dusk. I like to get to the fishing spots quickly to keep from losing what little time I do have. The cruse speed is nice and fuel burn is not too bad when at 2/3's throttle.
One thing I learned is to build the brackets as light as possible and with the least amount of setback as you can get away with on the 20’s. The 22” setback on this one lets the motor go to full tilt and has one inch of clearance fully up and two inches on the trim lock. The brackets I have done since are fully custom one offs popped from molds I’ve built. The time I spent modifying this one I could of built one that was 40 lbs lighter. This hull being a dual console sceptre I got away with the heaver bracket and 400 lb outboard but it would of been pushing it with a cc model.
Back on subject, I can say with the motor fully trimmed with the AV out of the water the boat when doing 55mph fast turning it you can hear the 14.5 dia vengeance prop slipping some. A little trim down keeps this from happening or staying under 50 helps also lol. The rev 4 or mirage props don't slip as much but you can hear as slight pitch change still. Any higher I think I would need a “low water pick up” lower unit as the water inlet is getting super close to sucking air. The rev 4 really likes being up at that height as it is a simi-surfacing prop but the smaller dia props all seem to pick up a 1-2 mph when trimmed up with the AV plate out of the water. I would recommend having the outboard set where you could go up an inch higher and down 2 inch lower if needed. Most can’t get their outboard high enough so keep that in mind. My bracket mounting ear is higher than most so you likely would be lower on a production style bracket such as an Armstrong. It is a “give and take”. You want the bracket floatation chamber as low as possible for floatation buoyance and still have enough height to get the motor AV plate up out of the water. The main measurement you want to worry about is the height of the AV plate is from the bottom of the hull when the out board trim is set so that the AV plate parallel to the hull bottom. I have found for 22-24” setback you want to be around 4-4.5” up from the hull bottom. A non-bracket hull on the transom can handle 1-1.5” up. Rule of thumb is to add 2” up from the hull bottom for each foot of setback on the bracket.

After adding weight to the front:

[fredbrad]

Thank you very much for all the explanation, I really appreciate it a lot

[natecert]

That is the best explanation of COG and a bracket I have read.

Thanks,

Ed

[Capt Terry]

Natecert-
Yes good info. I also suggest seeing my post "ESTIMATING CG SHIFT WITH HEAVY ENGINES" dated 9-24-16 snd the subsequent comments particularly by Bushwacker snd SSP Bill. If one takes my example snd changes the numbers that are applicable to them it should not be difficult if one can multiply and divide.

[flyingfrizzle]

Originally Posted by Capt Terry

Natecert-
Yes good info. I also suggest seeing my post "ESTIMATING CG SHIFT WITH HEAVY ENGINES" dated 9-24-16 snd the subsequent comments particularly by Bushwacker snd SSP Bill. If one takes my example snd changes the numbers that are applicable to them it should not be difficult if one can multiply and divide.

Bushwacker dose a great job on all the bracket informational postings, going back and reading anything he wrote on brackets and CG will be good information.

Originally Posted by natecert

That is the best explanation of COG and a bracket I have read.

Thanks,

Ed

Thanks, and God bless your situation currently. Me and my lady are praying for you...

Originally Posted by fredbrad

Thank you very much for all the explanation, I really appreciate it a lot

Glad I could help

[Topflitegraphics]

flyingfrizzle - Is this the same bracket you started with? It has a 30" setback according to the seller. I need to redo the transom on my 20' MA and am giving some serious thought to enclosing it and putting on a bracket but I need to do it on a fairly tight budget as my hospital bills from my heart attack just came in and darn near gave me another heart attack

[flyingfrizzle]

Originally Posted by Topflitegraphics

flyingfrizzle - Is this the same bracket you started with? It has a 30" setback according to the seller. I need to redo the transom on my 20' MA and am giving some serious thought to enclosing it and putting on a bracket but I need to do it on a fairly tight budget as my hospital bills from my heart attack just came in and darn near gave me another heart attack

Looks to be a Dusky built bracket but not sure if it is the same exact model as mine was. Mine was a twin outboard one with a built in splash well and it looks just like yours except mine was 24" setback and wider. Possible yours is a single version of the same thing just a little more narrow with more setback. Defiantly looks like a Dusky drive or bracket though.


One thing about them, they are built heavy. I haven't seen any cracks or anything of the sort show up on mine as sometimes you see gel coat cracks around the outboard tab. It has held up well and the only down side is the weight of it. I cut mine down a bunch but it still ended up a little heavy. It actually had balsa core in it which was light but the thick thick lay ups added the weight. Its not as heavy as it looks but it aint light either. I have started building mine from a full homebuilt mold now but modifying one to get you going on the cheap is defiantly an option. That was the main reason I done mine as I dint have much at all into building it. They work well and allow you to get the benefits of an bracket without spending the big bucks for it.