1972 Chieftain MKIV 25 footer ver 2

[bob johnson]

Re: 1972 Chieftain MKIV 25 footer ver 2

Brand new transom, 7 inch channel aluminum. Vertical brackets through bolted to transom and bolted to existing stringers, all rivits redone with high strength structural rivits.
View attachment 223633View attachment 223634View attachment 223635View attachment 223636

i am guessing you eventually will connect the large verticle sheets to the stringers....so i think the weakest link will now be the 2 rivets per rib that the stringers is held on by.....id bet the stringer was originallt designs just to support the floor.....not the forces and leverage of a heavy cantilevered outboard.... the stringers are .....what..... 1/16th thick aluminum?? maybe .08"

i have an outboard bracket and have a plan to rivet ( maybe even tack weld) 1/4" X 3" aluminum angle with wedges welded to the top to make a flat horizontal surface to attach the braces that go up at an angle to the transom, onto at least 4 ribs.

i think if I were you.... Id bend some 1/8th aluminum sheet to fit along side the insides of your plates and allow enough coverage on your ribs to get 4 rivets on each rib....and id want to see at least 2 feet of that on each side of the trough...

i am thinking you may start to pull your rivets out of the stringers-ribs JUST trailering the rig down the road with that big cantilevered motor.

you have to over build, because the factory I\O had very little forcs on the transom and little weight hanging off the back


good luck

bob

 

[Sc25175]

Re: 1972 Chieftain MKIV 25 footer ver 2

What the pics don't show is the HDO plywood deck tied into the stringers and the channel iron. I basically decided to go forward with a bracket after I read someone on the forum built a homemade bracket and all they did was bolt one piece of channel on the inside of their existing transom(read old) and their motor is heavier than mine. He has been running for a couple a years now with no issues. I also quizzed the manufacturer of the bracket and they have seen hundred of these done and the only requirement they insist on is a solid(read new) transom at least one and one half inch thick. I doubt there will be any flex based on how it is bolted up. My only concern is the entire back of the boat rips off but when you look at the transom of aluminum boats the only difference I can see is the knee they tie from the transom into the bottom of the boat, the ones I have seen are not all that large.

I agree this was not professionally engineered but all my buddies who are very mechanically inclined are telling me I'm good. When I splash this baby I am going to post a video so hopefully I won't be posting a worlds funniest video

 

[jasoutside]

Re: 1972 Chieftain MKIV 25 footer ver 2

What you have there looks very strong to me and I highly doubt you'll have any issues.

But, if I were in your shoes, I'd do my best to bolt up a pair of knee braces back there, just to sleep well at night eh.

 

[bob johnson]

Re: 1972 Chieftain MKIV 25 footer ver 2

welllllll..... need i only point you to our favorite aluminum manufacturer??? the outboard version of a 22 ft starcraft NOT ONLY has KNEE braces, it also has a MONSTER splashwell that has a kazillion rivets all around that offers support from the sides to the transom, and the sides to each other ., And that is for a transom mounted outboard...not even a cantilevered OUTBOARD on a 30" set back bracket.

not only had I planned to run two 2" square 1/8th" thick tubes from the heavy C channel( like you have) to the special brace attached to at least 4 ribs( that i spoke of earlier) I also planned to add similar tubing to run from the transom at an angle to the gunwales maybe 3 feet up that ties into top strip . which is riveted to the inside panels that bolt to the floor!!

KINDA LIKE the splashwell is tied to the gunwales

I am sure on the water, you could get away with sooo much more....but your problem will be trailering that rig...... 350-450 lb motor will be hanging 30" off the back trying to rip the transom away from the sides and the floor


and it will do it little by little.


just go find some pictures of what a 21 or 22 foor starcrafts splashwell really lookes like




good luck


bob

 

[Watermann]

Re: 1972 Chieftain MKIV 25 footer ver 2

Steve, I'm not piling on just have a question about your Chief. It's a 72 and I didn't see any pics until your deck was already installed. Just wondering what if anything you did in the way of hull stiffeners or splash rail braces or did you have any issues like so many of us do with our older SC's?

 

[Sc25175]

Re: 1972 Chieftain MKIV 25 footer ver 2

Not 100% sure what you are asking but the hull was in perfect shape. I agree that the stringers are not super thick .100 but they run all the way to the bulkhead and between the boxing in under the deck and the way I tied the deck into the transom and the stringers I still don't think I'm going to have a problem. I had three 230lb guys standing on the swim platform portion of the bracket and there was zero deflection.

 

[jbcurt00]

Re: 1972 Chieftain MKIV 25 footer ver 2

Sounds GTG ^^^

Looking forward to seeing the hull in her new white dress....:watermelon:

 

[bob johnson]

Re: 1972 Chieftain MKIV 25 footer ver 2

Not 100% sure what you are asking but the hull was in perfect shape. I agree that the stringers are not super thick .100 but they run all the way to the bulkhead and between the boxing in under the deck and the way I tied the deck into the transom and the stringers I still don't think I'm going to have a problem. I had three 230lb guys standing on the swim platform portion of the bracket and there was zero deflection.

nice......that's due diligence!!! I didnt think my islander stringers were that thick. take lot of pictures please. I still needt to put mine together...maybe this summer!

bob

 

[Watermann]

Re: 1972 Chieftain MKIV 25 footer ver 2

Steve here is a pic of my Chief with the hull stiffener/splash rail braces in place. The braces are a later retro fit to the older 70's models that didn't have them due to the lack of engineering on SC's part making the spray rail a weak spot that cracks the bottom of the hull at the rib ends and the rail itself. Here is a pic of my braces in place, you can see how they tie the bottom and sides together.



Bluefin fabricated his own as well in his SS thread. Anyway I was just wondering if you had any cracking or problems in that area.

edit: and Bluefin's SS.

 

[Sc25175]

Re: 1972 Chieftain MKIV 25 footer ver 2

OK now I understand the question. On my 25 footer there is actually some sort of insert that is riveted to the inside of the hull and tied into the internal stringer and deck structure.

It is hard to see but if you look at the hull you can see there is an inner piece and the piece is solid riveted to the hull.

Time will tell but when you take everything I moded in total this is a super strong structure.

 

[Watermann]

Re: 1972 Chieftain MKIV 25 footer ver 2

OK now I understand the question. On my 25 footer there is actually some sort of insert that is riveted to the inside of the hull and tied into the internal stringer and deck structure.View attachment 223792

It is hard to see but if you look at the hull you can see there is an inner piece and the piece is solid riveted to the hull.

Time will tell but when you take everything I moded in total this is a super strong structure.

From what I can see it sure does look like a good design that's well built!

 

[Sc25175]

Re: 1972 Chieftain MKIV 25 footer ver 2

First coat of white


In the bow area I am going to have a line where I painted the bottom and now am painting the sided. In retrospect I should have followed the chine all the way up. Any ideas on how to blend these two areas together?

 

[Watermann]

Re: 1972 Chieftain MKIV 25 footer ver 2

First coat of white
View attachment 223943

In the bow area I am going to have a line where I painted the bottom and now am painting the sided. In retrospect I should have followed the chine all the way up. Any ideas on how to blend these two areas together?

Nice progress with the white dress. :thumb:

Once dry I would feather out the bottom edges of that first coat then prime where sanded if needed. Re-tape following the splash rail for the last coats on the sides. Then go back to your 2nd side coat. I wouldn't worry about the top edge just shoot more of the bottom color over that first side coat. If that makes sense.

 

[barato2]

Re: 1972 Chieftain MKIV 25 footer ver 2

my 2 pesos': don't worry about it, it will look fine. what you have now is the classic paint scheme for a big cruiser, and you got the Mini Tinnnie Bertram or Hatteras there. i think it would look weird if you tried to follow the line o' the chine.

 

[classiccat]

Re: 1972 Chieftain MKIV 25 footer ver 2

DANG! DAT'S ALOTTA BOAT TO PAINT!

I wonder what it would translate to in "rattle-can" units :lol: I guess we'll find out when jas paints the 26'er!

+1 what bruce said...Looks good just like it is! But it's your opinion that counts most :thumb:

 

[Sc25175]

Re: 1972 Chieftain MKIV 25 footer ver 2

So far two full gallons of primer and I am breaking into my third gallon of white which might just get me there. I am thinking less then half gallon of navy blue for the boot stripe and side detail.
Should have her done by next weekend. WoooooooooHooooooooo;-**

 

[Weep'n Willy]

Re: 1972 Chieftain MKIV 25 footer ver 2

She is looking real good Steve. A major milestone for sure. Are you gonna have her done by summer and on the water?

 

[Sc25175]

Re: 1972 Chieftain MKIV 25 footer ver 2

That is the goal. Still have to do the mechanicals including hydraulic steering. I probably won't have the cabin finished but I really want to see if my bracket is going to work and how fast she will go.

 

[barato2]

Re: 1972 Chieftain MKIV 25 footer ver 2

you'll find that the fresh paint really helps with the motivation and you'll fly along now. and once you have a running boat and you're into the "furnishing and trimming out the cabin" stage, you might find that the Admiral really gets interested in diving into the project. i'll be watching your progress, esp since i'm also curious about the bracket.....not much room fer my big clumsy feet in the Starchief cockpit when i'm sharing it with a cast iron lump. (of course, the Chevy tells me I'M the lump....:lol

 

[InMotion]

Re: 1972 Chieftain MKIV 25 footer ver 2

So far two full gallons of primer and I am breaking into my third gallon of white which might just get me there. I am thinking less then half gallon of navy blue for the boot stripe and side detail.
Should have her done by next weekend. WoooooooooHooooooooo;-**

Great progress man! Nice work. And ya... that's aloooooot of paint!! But she's lookin' sharp!

Jim