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Hulls for c/m(caddy)

Hello everyone, my names Chuck. I live in Citrus County. I just got a big block caddy motor(for free 😍)and want to build a airboat. What do you look for in a hull? I seen a cottonmouth 13.5 x 7.5 just didn’t know if that’s too narrow. Was wanting to go aluminum but my pockets aren’t going to let that happen. If someone could point me in the right direction that would be splendid...

Don’t know exactly how long it’s going to take me to piece together a airboat but looking forward to talking with y’all and hopefully learning a lot along the way!
check out the marty bray hull if you want fiberglass. he's making a 13x8 now. i think he has the only hand layed boat around
It really depends on what you want to do with the boat and what your experience level is. Smaller and lighter is going to run better and should be decent on dry ground if you set it up right, but requires more experience and is not as safe of a boat in deep water. On the other hand, a bigger hull will be better for carrying more passengers and cargo in deep water and will be safer, but likely won’t run dry ground.
Thank you Striker, I’m brand new to airboating been on a couple never drove one. But I’m collecting info right now. I have a chance to buy a decent 13.5 x7.5 cottonmouth. Just don’t know if it’s too small! I’m really trying to not jump the gun and buy something I will dislike or put me and my family(4 of us) in a bad situation. I’m going to fish off of it but I would also love to take the family on Saturday runs you know just enjoying nature and cold refreshments. That being said I’m trying to budget friendly as I’m sure this will be a 5-6 month project with work and family. I’m going to do stainless rigging. And direct drive for sure since its a caddy. I figured my next step is finding a decent haul and starting the build while figuring out what to do with my engine like the thought of a Mr.Branch motor but don’t think spending $6600 for him to build my motor is a good first choice. Figured get my feet wet then I can always get him to build it. Any input you or any of the other members give is great!
All of the info that Striker presented is factual and should be kept in mind. There will be no point, ever, that information is not relevant.
Power to Weight Ratio is also another inescapable fact that influences most decisions.
This is why a Caddy works well for a Direct Drive; it can produce measurably better HP and torque compared to most small blocks while not making the weight penalty an insurmountable issue. With that having been said, every old Cadillac you come across is not a venerable 500.

While all the input you've received up to this point seems to be good advice, there looks to be the assumption that it is in fact a 500 that you have and are going to use. There is nothing wrong with that, BUT is something (imho) that you definitely want to confirm before you go hull shopping. There is a VERY radical power AND longevity difference between a later 425 and an earlier 500. Choosing the wrong hull for the wrong amount of power could leave you forever crippled where performance and/or safety issues are concerned. A 472 can and will work acceptably as long as your expectations are realistic. We have one we've been running for over ten years. It's on a 15' RiverMaster and surely is not a mountain goat by any stretch of the imagination, but does run loaded for a Saturday at the spring with enough to sink a smaller hull; and yet . . . is quite nimble if I'm on it by myself.

The block casting number is behind the intake, at the top (near the oil pressure sensor). If it is a ***5200 block, then it is a 472 or a 500. After that confirmation, measuring the stroke (with a straw, coat hanger, or whatever) will tell you which it is. A 472 will measure a little shy of 4 1/8 and a 500 will measure more than 4 1/4. There are a couple other possibilities, but I don't remember all that off the top of my head. If you check it in that fashion and arrive at something different, report back and I'll go digging a little bit.

Needless to say, learning to exploit the [Search] feature on this board will yield volumes of information about this subject matter.
It’s a 5200 block I checked before I even loaded it in my truck. It came out of a 76 Cadillac Eldorado with 86k which I’m pretty sure it was a low mileage car the interior was clean. And the windshield wipers weren’t loose. I picked one up and wiggled it to see how much play it had and it was pretty tight. A buddy buys these things and demo derby’s them with ls motors! I was hoping to get it on the engine stand this past weekend and start the process of digging in. But wife and life had other plans! I have used the search bar a good amount already So I knew about the 5200 casting. I will let everyone know more as I continue!
Odds are great it was the original engine @ 86k miles so . . . great find!
That would make it a 500 with the later open chamber (low comp) heads.
But then you already knew that since unlike most folks, you [Search]ed first, and posted second. :thumbleft:

I know this isn't much help, but since you haven't had any other Cottonmouth comments, I will throw this out there anyway. A buddy of mine had a 13 footer like you elude to, that had a 351W on it. It must have been built right, because it ran like it. That hull did not have the motor (prop) well cut out of it, so the rigging was taller than most of what you see. Consequently, it felt quite 'top heavy' to anyone not an experienced airboater. Unfortunately, his wife never got used to it and over time he sold it because she said it was 'too tippy'. :?

Along the way, cutting out that well has been debated here at least once. I'm sure you can find it knowing how to look. I don't really have a strong opinion about that either way, although it seemed to me like a marketing tactic more than a functional improvement. Were I going to rig one with a Caddy for four people, I would most likely remove it because doing so would help relieve the 'tippyness' that may make Mom and the kids a little nervous. It would also afford you a little more elbow room when building your rigging.

If it is within your means to do so, I would not have any debate with myself about ordering a Marty Bray hull and would do that asap in order to minimize my delivery time. His hulls are as stable and as well built as any that you will find (<-- likely an understatement there) and not gain an excessive amount of weight while attaining that end. The only question I would need to answer before I pulled that trigger would be "Am I going to stay DD for the life of the hull or might I add a gearbox later? The reason I point this out is because if you think you might add a gearbox you would want to opt for at least a 14 or maybe 15 footer simply to increase your safety and comfort level while toting your family. When you are toting four people with a gearbox anything smaller starts getting cramped and sitting low enough in the water to potentially be a concern.

Being new to the sport, you are likely unaware of this, so I will share this in the event a new hull is not in your cards. In the beginning, Marty Bray was the man who made the original River Master hull molds. Dick Hoffman made those hulls in Inverness (using those molds) for years. They were known for their stability and strength, and were debatably the standard for 'glass hulls for a number of years. After Dick passed away, the molds were sold and ended up in South Florida. To my knowledge they never went back into production. Somewhere along that timeline Marty Bray made new molds with improvements and modifications to that design and has been making them ever since. The point being, if you are looking for a used hull and can find a River Master that is in good or restorable condition, that would likely be the next best thing to having a Marty Bray hull. I have two of them, so can attest to all that first hand. You don't see many of them for sale anymore but they are out that thicker than old Caddy's with 86k miles, I am sure.
Well that is three experienced airboaters tell you the Bray hull is the strong choice. If that don't point you into the right direction I don't know!

The standard mold short 15 (15ft 4inch I think) is a great universal hull for DD or gear drive. I would order it without rod boxes for DD to save $ and weight. Marty was running a Caddy direct drive 18ft boat with an extended front deck but my last visit with him he was planning to derig and give his new wide hull a try. His 18ft ran dry by the way but he had a amped up engine so maybe talk with him about your needs.

I have net fished in open inlets with my 15ft 11inch so that should give you an idea of their stability
I feel if I was to pull the trigger on a new haul and spend that 3000-4500 I would go aluminum over fiberglass and just spend a little bit more. But I was trying to stick with used because Of the cost factor And the ease of finding a used fiberglass boat and I can do fiberglass work (even tho I hate it)! I did check the stroke tonight and it’s a 500 no question about it! And as you have said in a lot of threads the low compression you can run pump gas which I think is the best for me. I will probably just start with a timing chain new oil pump and cam rebuild the q-jet just to get the boat built and run it. Then eventually pull the motor and rebuild. The cottonmouth I could have got for $500 came with a double seat a single seat and a fuel cell. But I waited too long 😕
Plenty of old hulls right in your area start looking.

Anyone who has been around the block has seen this before so heed the advice and save yourself the grief. For a newbie a stable boat is best.

Try at the old Pemberton lot they had some old hulls out front not sure what make. There are new people running the place and are actually building a glass hull now. The older fellow who is running it is named Wayne and he has a lot of Cadillac experience we have traded parts in the past. US41 / Pemberton Ln it is 1/2 mile south of FloralCity Airboats on east side of US41.

Big difference in money between a new glass 15ft and an aluminum hull in todays market. May get 2 glass hulls for the price of an optioned aluminum boat and welded hulls are heavy.

I will keep an eye out for a 14/15 used for you
I ran a caddy on a 15' Hoffman rivermaster for a few years. The rivermaster just did not hold up to the rocky area I fished on the gulf. I bought a 14x7-6 Alumitec hull. Ran better but sat lower in the water, didn't seem to float as well. I met marty at hagan's cove right after he built the 18' boat with a caddy, it ran very well. My 15' boat would cross dry where my 14' boat would run dry without much issue. I also only had a .020 over 472.

Swamp my glass hull was way heavier than my aluminum hull. Just depends on how they're built in my opinion

What do y’all think? Too top heavy.... easy to sink? That’s what I’m thinking but also for $1500 😳 it would just be a beer boat at that point probably
Unsolicited advice:

Stop looking at the price

Start looking at the quality, diversity and safety of the desired platform.

May be a great deal if not a ragged saltwater hull but even so that will be very limiting on your desire to haul the family. It would be an easy push for a 472 or 500 but not very diverse in multi-role use.

The 14-15 Bray or MarshMaster would win favor with your family and be a bit more capable to fill different future needs.

My 2 Cents
Chucksterinthecc said:

What do y’all think? Too top heavy.... easy to sink? That’s what I’m thinking but also for $1500 😳 it would just be a beer boat at that point probably

If I’m seeing the same thing you are, that’s a 12ft boat with low sides. No way I would put a caddy on that. It will be very unstable and probably will not float well. I would guess that water will come over the transom.