24 open outboard conversion started

[bob311]

Well,
I have talked about this for a while and it was the original intention when i picked up my 24 open but it looks like its finally time to start the conversion. My last outing the lower unit made a horrible growling for anything above ide and when i drained the oil it was a solid milkshake full of metal shavings. SO, i pulled the trigger yesterday and bought a Viking outboard bracket with 30" setback and 13* offset, I figure I can wedge it a degree or 2 if needed.

Here is my plan for the transom.

#1 - sand and remove everything off the transom
#2 - drill and taper all holes, fill with thickened epoxy, both inside and out of the transom
#3 - run a 45 degree router around the keyhole and glass in a plug with marine plywood
#4 - install a 1/4" 6061 aluminum plate on the outside of the transom. the plate will have shallow strut welded across it to add strength and also provide place to mount any future electronics, pumps, typical transom shit, this way nothing will ever be drilled into the transom again...
#5) drill the holes for the extension bracket and seal them with glass and stainless steel sleeves. (no exposed wood)
#6 - Install a 1/4" aluminum backing plate on the inside of the transom, boxed in with angle plates and 1"x 1/8" vertical strips welded to make it rigid.
#7 - tie the backing pate to the engine stringers with a cross bracket and turnbuckles.

that's about it for now, honestly im looking for the quick and easy way to get this done before April.. which will be tough... let me know your thoughts. Also, how do you guys feel about skipping, the keyhole patch since it will be sandwiched by aluminum and sealed? that would save at least 2 weekends.. Going on the back of it will be a yamaha ox66/hpdi 250hp that i have standing in my dads garage waiting for this build. Its a 3.3l hpdi block with ox66 front half and ECU. no more high pressure fuel issues/ detonation on cyl #2 and more torque than the smaller ox66 250.

ill be putting up on here all of the old running gear soon including the engine (rusty AF) but runs well $1000 bux. the drive for parts $200 bux, with transom shield, and the steering wheel w/ cable $100 bux (cable less than 1 year old and smooth). Other items going up for sale is a brand new affordable fuel injection for the engine that was never put on. its a closed loop o2 system so there is no o2 sensors to worry about.

 

[SilentViper]

Look forward to seeing your performance numbers when it's all done. I'm on the fence on doing this to mine. If this inboard gives me one more bad day this year, i'm buying an outboard, probably yamaha 300/350.

There are other threads here of guys outboard converting their 24 opens. My Favorite: https://www.bdoutdoors.com/forums/threads/1980-24-skipjack-opened.609920/

Disclaimer: I'm by all means not an expert, but here's my take.
Alot of my opinions are gonna stem from boating youtube channels like BoatWorks Today and west systems manuals: https://www.westsystem.com/instruction-manuals/

Steps
1) Fine
2) Fine
3) if you want the plug and transom to be structurally sound you're supposed to grind in a ~1:12 feathered edge around your bonding joint. if your fiberglass is 0.25" thick you'd need to feather 3" around it, allowing new layers of fiberglass to bond to each other and the old glass.
4) Why? if you're fiberglassing the keyhole plug properly inside and out the "aluminum plate" will just be part of your bracket itself.
5) Sounds overkill, typical method i've seen is Drill Fill Drill. Drill way oversize, fill with thickened epoxy, Drill it to size again.
6) plate or effectively large washers on the inside is fine i think, spread the compression load from the bolts.
7) I'm not sure turnbuckles are gonna help correctly. If the transom can't support the engine statically the force of rough waves and a 250 hp motor torqueing on the transom isn't gonna be good for it either. if the engine is pushing on the transom wont the tension on the turnbuckles go down?

I'd shy away from not plugging the keyhole. i saw a 24 open someone did an outboard conversion using alum plates like you're describing sit on craigslist for like 6 months for only a couple grand. no one wanted to touch that with a 10' pole, risk isn't worth the saved effort. Keyhole plug doesn't have to be absolutely perfect fit, but close enough that just epoxy is needed to fill the gap, then fiberglass over the outsides.

My understanding is that Armstrong recommends 1 inch of transom thickness per 100 horsepower, the transom on my boat being only 2" (0.25" fiberglass inside + 1.5" of wood + 0.25 fiberglass outside) would need to be beefed up to support a bracket with 300 off the back. yours is borderline for a 250 according to their guidelines. My theoretical plan is to either:
* add a layer of wood and glass making the transom 3" thick below waterline.
* add a 1" thick x 6" deep x 84" horizontal brace/knife board/shelf just above the height of the bracket to add some rigidity to the transom.
And add knees from the old engine beds up to the transom, and small knee just above the drain plug for the base of the bracket to transfer force into the transom into the hull keel.

Again, i'm no pro, i just watch them on Youtube. lol. 40Grit, SB Surfer, Towerfab, Jeff hull are all literal professionals around here, get a hold of them and pick their brains. The last thing anyone on a skipjack forum wants to see is your dream boat have major issues out at sea because you wanted to save a weekend of fiberglass work.

 

[bob311]

Thank you SilentViper,
sounds like the keyhole pluged at 1:12 is the right way to go. After one year i will forget about any extra work i put in, but wouldn't forget about a big hole in the transom..

#4 - The reason i want an aluminum plate across the back is so i can have the shallow strut across the transom for future mounting. this would eliminate any need to ever put a hole in the transom again and also make moving a pump, ducer, or trim tab much easier.

#5 - noted, and will take into consideration, this is how i rigged my sanger cat and have had good results putting it through more abuse this boat will ever see.

#7 - I was really hoping the Skippy transom would be strong enough for just some turnbuckles and tie braces. But, it sounds like it will need some extra meat. In that case, what do you think about a layer of mat between the existing and new wood for bonding, and 3-4 layers of 1808 biax for the new inside skin? Its not that I'm bad a glass work, i just hate it with a passion.

 

[SilentViper]

#7 - I was really hoping the Skippy transom would be strong enough for just some turnbuckles and tie braces. But, it sounds like it will need some extra meat. In that case, what do you think about a layer of mat between the existing and new wood for bonding, and 3-4 layers of 1808 biax for the new inside skin? Its not that I'm bad a glass work, i just hate it with a passion.

I did exactly that patching rot in my transom around the keyhole. I was gonna post pictures of mine, but I guess i didn't take any of the process. Seems to be holding up perfectly. Your transom might be strong enough, i dont know your boat. But ~40 year old wood is the last thing i'd want to risk & trust.

I'm in the same boat on glass work, the end result is nice, the process sucks. Finding cheap painters suits on amazon to keep clean is key for me, and a good full face respirator mask + headphones for grinding makes it much more bearable.

 

[SilentViper]

By happenstance Florida Sportsman posted a very succinct video of how I described filling the transom in for a bracket.

 

[bob311]

By happenstance Florida Sportsman posted a very succinct video of how I described filling the transom in for a bracket.

This is great!

 

[bob311]

@SilentViper,
Did you use Polyester, Vinylester, or Epoxy? Im leaning towards the vinyl for cost and aviailability on both the cloth and the resin. I've used the pro-set epoxy more than id like to admit but that was already on a composite lay up where poly and vinyl weren't an option.

 

[SilentViper]

I used West Systems Epoxy. but that was back when it was $100/gallon not $140.

If i had planning skills and forethought i'd buy epoxy from US Composites.

 

[bob311]

Thanks,
ill check out US composites. I used to get my epoxy from revchem and i think pro-set is around 200 a gal with out the hardener.