Does anyone know what alloy a 1974 Chieftain hull is made from?

[adamjr]

This may be for a completely stupid reason so I am hoping to get some input over and above the original question with regard to the reason for asking it.

I have a 1974 18' Chieftain. The model I have is an O/B model. I have looked at a lot of restore threads and aside from the transom skin itself it looks like there are no real stringer or bulkhead differences between the I/O and O/B models.

With that in mind I have considered converting my boat to an I/O model. I have opportunities all the time to pick up old boats with fully functional Mercruiser 120's and 140's for near nothing. My hull plate says the max HP is 140 so as tempting as a 165 would be I don't want to risk that.

From looking at the different threads it appears to me that the aluminum skin on the O/B models is just a little taller then the Mercruiser keyhole cut-out. It also seems to me that for the most part the real strength of the transom comes from the 1 1/2" laminated and encapsulated plywood more so then the skin. I have a metal supplier that can provide just about any alloy at a competitive price that a person might want. My thought was that I could make a template of the cut out area of the transom from which the supplier could cut my extension. I can then mig in the new piece of aluminum in order to make the conversion as well as fabricate the cross brace that goes over the top from gunwale to gunwale.

Am I out of my freakin' mind or is this reasonable? Are my assumptions (yup, I know about what you get when you assume) correct about the strength of the transom coming from the plywood more then the skin?

Thanks in advance for kindly telling me I'm correct or gently telling me I'm out of my freakin' mind.

Adam

 

[CheapboatKev]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

Adam my friend
You are out of your freaking mind!
There are paaaaa-lenty of frozen block junk motor I/O Starcrafts out there for you to go to that much trouble.
For all the work and planing it would take...I just dont see this as being feasible.
You do know you are thinking of the exact opposite of everything Holy in the Church of Tin?

 

[Huron Angler]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

I believe they used 5052 aluminum. The brochures link in my signature will tell you more details.

As far as your idea goes, it is ambitious which I like...but I'd just buy an outboard for it and have fun

 

[barbosam]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

I don't know this as a fact but the hull is most likely made from 5052 aluminum. This is the most common marine grade sheet metal. If you can't get a definitive answer 5052 is your best bet, I'd put money on it.

And you are out of your mind, why would you ever convert to an I/O? That's a disgrace! Do what you want, I'm just ruffling your feathers a little, everyone has their preference. Most people convert from an I/O to an outboard though. whats your reasoning?

 

[ezmobee]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

The outboard models are much more rare. I agree you'd be crazy to try to convert one to I/O. Just go find an I/O hull.

 

[GA_Boater]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

A few of concerns. This first one - I have no expertise with aluminum welding, but every time I read about welding AL, those with expertise warn against it because the AL loses its temper and can become brittle. Just a thought.
Secondly - Do you really want to lose about 3 feet of cockpit to plant an I/O in an 18 footer?
Third - Please don't tell us you might pass on a Mercruiser and drop in an OMC stringer. Although the design of a stringer drive (ignoring all the gotchas) would be better suited because the forces are through the boats stringers instead of the transom.

Only the first two are concerns. Unless you really are out of your freakin' mind. LOL It wouldn't be a boring project, that's for sure.

 

[adamjr]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

I guess I'm just nuts I guess. Thanks for the input. I always liked straight up GM motors when it comes to the ease of working on them. I have an outboard on my old Clipper Craft but I've always wanted an IO.

I was thinking of 5052 for it's flexibility since that's what the fuel tank inmy Clipper Craft is made of.

I know it's a little nuts and ambitious. In the long run I will probably just leave it as an outboard. It just seemed like a neat project to me. Mostly I think I just wanted to see if I could do it on the low dollar amount I have so far layed out as well as what I have beem offered for nothing and near nothing.

 

[jasoutside]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

Original question - yah, 5052 alum.

OB to IO? Nah, no reason for that.

Though there are lots of good reasons to want an IO over the OB

I'd agree with EZ if you really want one. Just sell what ya have there and grab another cheap

 

[dozerII]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

Secondly - Do you really want to lose about 3 feet of cockpit to plant an I/O in an 18 footer?

Just to confirm, I have a 18SS I/O and a 18SS OB sitting side by side in the garage, the only difference in interior room between the two is, the engine cover on the I/O sticks 6 inch further forward than the splash well on the O/B model but the I/O has a seat on either side making more usable interior space in the I/O model than the O/B. I'm Just saying?
Glen

 

[jasoutside]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

making more usable interior space in the I/O model than the O/B. I'm Just saying?
Glen

I was going to mention that as well but I'm not really one to stir the pot ya know.

 

[dozerII]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

i was going to mention that as well but i'm not really one to stir the pot ya know.



:d

okay?:facepalm:
Glen

 

[jasoutside]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

okay?:facepalm:
Glen

Yah, ya know how some guys get all hyper sensitive about it when you say mean things about their precious OB's....

But like I said, I'm not one to cause problems around here

 

[MichaelP]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

"I'm not really one to stir the pot ya know." Yea Right

Welding aluminum reduces the yield strength of heat treated grades back to what it was before heat treating. ie 6061-T6: T6 is the heat treat designation so if you weld just straight 6061 there should be little or no "weakening" of the material. So, If you go with the recommended 5052 that isn't heat treated you should be fine. However, welding will introduce stresses in the weld zone and your fabricator should know how to releave them.

I checked out space differences too and I agree with what was stated above. I'm shortening my splashwell on my OB to make more room. I might be able to send you shop drawings of the new one.

I think your nuts to go IO with that hull.

Once the pot has been stirred it cannot be unstirred.:facepalm:

 

[paparoof]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

So we'll never get over the I/O vs OB thing, but I'm impressed there seems to be uniform agreement that our dear friend Adam and his freaking mind have parted ways. And trust me on this Adam, we mean that in the nicest way possible. Most of us haven't visited our freaking minds in a long, long time.

What's your true goal here? If you're just after an I/O, just go buy an I/O. If your real intention here is the experience of a major re-engineering project, then by all means, go for it! Just do your homework first and take lotsa pictures and get 'em up here. That would be a truly unique project and we'd all love to watch as it happens.

 

[barato2]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

it's absolutely 5052. Starcraft brags abt that in the orig brochure that came with my boat....5052 is the most corrosion resistant alloy.

Adam, why don't you swap your OB boat with someone who has comparable condition I/O? as popular as OB cruisers are on here, i bet you could find someone willing to consider it. or sell it and get an I/O boat plus some profit to spend on the refurb?

i assume you have a spool gun if you're talking about using a MIG for AL. if so, remember, there is option #3: build a pod for the OB and gain back that lost 3' of your boat

 

[GA_Boater]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

My comment about losing 3 feet was because of two things;

1) I forgot that SC uses the "No splashwell is too big" splashwell rule, which would resulti in a increase in cockpit length. Even my 16 footer has huge SW.

2) I wasn't thinking clearly as I was going

 

[jasoutside]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

Yur funny GA

 

[CheapboatKev]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

"I'm not really one to stir the pot ya know." Yea Right

Welding aluminum reduces the yield strength of heat treated grades back to what it was before heat treating. ie 6061-T6: T6 is the heat treat designation so if you weld just straight 6061 there should be little or no "weakening" of the material. So, If you go with the recommended 5052 that isn't heat treated you should be fine. However, welding will introduce stresses in the weld zone and your fabricator should know how to releave them.

I checked out space differences too and I agree with what was stated above. I'm shortening my splashwell on my OB to make more room. I might be able to send you shop drawings of the new one.

I think your nuts to go IO with that hull.

Once the pot has been stirred it cannot be unstirred.:facepalm:

But it can be allowed to settle....

 

[adamjr]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

More then likely this will remain just a hair brained scheme.

Last night I had a long reply after EZ and GA's replies but for some reason my work laptop logs me off of Iboats forums after only about 5 minutes and I have gotten out of the habit of higlighting my posts and clicking copy prior to posting in case such things happen. It was getting late so I left this until now.

EZ, you're right.

GA, I said in the deleted post pretty much what Dozer said. I would have put a fold down jump seat on either side of the dog house.

The thing I like about this site is that I can expect both useful information as well as good natured ribbing. Being able to recognize when you're over your head is a valuable skill I've learned over the years. I don't necessarily think I'm over my head on this project but I do accept that it would present considerable challenges. Ad to that the cost of doing it and I'd have to agree that if i want an IO model I should go out and find one.

At least I know better then to think I'm going to graft together the hulls of two 26 foot tinny's and make a 36 foot offshore racing tinny. I just found that post when I was researching the alloy question. What an odd braggard that guy was.

I got a great deal on this boat even though it is going to present an interesting challenge due to a moron of a previous owner. I was going to begin the process to remove the deck beginning with drilling out the rivets. I pulled the carpet and lo and behold I see NO rivets ANYWHERE. I also found when I pulled the carpet from the sideboards that the deck meets the sideboards rather then the sideboards resting on top of the deck. The sideboards are also not fastened to the deck which I thought was strange. I got my pry bar under the sideboard and lifted a little. My previous observation was right. I went into the cuddy and sat down on the middle locker and staired at the deck. Two layers of deck with a massive wad of adhesive smushed out between them.

My worry here is how to remove the deck without destroying the stringers. So my thought on this is to put a plywood blade into the circular saw and cut a rectangular hole down the middle deep enough to remove 2 layers. Next to change the depth to JUST more then 1 layer (about 1/16") and make cuts from port to starboard about 8 inches apart and use a chissel to separate the layers. I am pretty resigned now to the probability that I can kiss the idea of having templates from the original deck goodbye.

Does this sound like a reasonable way to go about things?

 

[rheagler]

Re: Does anyone know what alloy a 1974 Chieftain hull is made from?

Your floor removal idea sounds reasonable. I would use a regular combination blade on the saw, plywood blades are made to leave a smooth cut so they are notoriously slow. You just want to get the material out. I would also just set the saw to cut ALMOST through both layers. Chances are the original layer is deteriorated enough that you will be able to just bust it off the rivets without seperating the layers. Usually with demo jobs the best thing to do though is have multiple methods brewing in your head. If the first choice isn't productive, try something else.
As far as templates, you really shouldn't need them for your hull. All you really need to do mark the sides of the hull along the length, starting from the transom, say every foot. Measure the width at each set of marks, and transfer that to your new floor material working off a center line. I hope this makes sense. If not I will be happy to try to explain it better.