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Thread: Modifying a boat trailer for an airboat

  1. #1
    Super Moderator Corky's Avatar
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    Question Modifying a boat trailer for an airboat

    It's time to deal with my boat trailer...As you can see it's a little beefier than I really need for my mini...

    The good:
    It's got surge brakes, six lug axles , a spare tire, and the frame is in overall great shape..

    The bad:
    The brake system looks like it hasn't worked since 1989...The master cylinder is dry and half full of {?} in there..The wheel cylinders aren't much better and one brake shoe gave me the lining it didn't want to keep when I removed the hub... So needless to say the brakes aren't getting massaged into doing their job at this point...{I knew they didn't work when I bought it}

    All the lights need replaced...
    The boat would sit too high on the trailer using the roller system in it's current state...

    Here's the pics as it sits so you can get an idea of where I'm starting..
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    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  2. #2

    Re: Modifying a boat trailer for an airboat

    Interesting.
    I have to build a trailer for mine too.
    Keep the progress report coming.

  3. #3
    Super Moderator Corky's Avatar
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    Re: Modifying a boat trailer for an airboat

    Here's where I'm asking for opinions and advice...Any and all thoughts and suggestions/discussions would be a great help...

    A} As you can see the frame crossmembers are arched downward making this trailer less desirable for a flat bottom airboat...OK I can deal with that...But the rails are spanning 7ft between them{front to back}...The roller bunks would be 5ft...Too short...And the bigger question..I really need about 11ft of rail my flat bottom is 10ft{+}until the front rake so I'd need something to make up the difference even with the roller bunks ????

    B} My 14ft mini will fit on this trailer leaving the front tongue stop,spare, and winch intact...And the hull will be even with the back trailer frame rails leaving the rudders overhanging the back...Is this a good set-up ? I could possibly move the boat {and rearrange the front stuff} so the rudders would not be exposed behind the frame rails I do have enough room to do that {I think}..But it appears it's common to leave the rudders hanging out the back and exposed to Mr.Tailgater and getting rear ended would mount the rudders on his hood ???

    C} I've taken the original rollers off the boat and left the mounting brackets on the crossmembers... And have moved them in to where they need to be spaced apart so they match up to the hull's stringers...As they sit in this pic they're about 2 inches below the side frame rails...Couldn't I just add a 2x6 inside these brackets and span them for my rails ???

    Here's a few pics of where I'm at now... I've included a blue highlighted pic showing what I was thinking for the {carpeted}rails and the side fenders.. .
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    Last edited by Corky; 06-27-2017 at 07:24 PM.

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  4. #4
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    Re: Modifying a boat trailer for an airboat

    this is just me but i would get rid of the brakes and the over kill hitch and bolt a 2x4 or 2x6 where the bunks go and bolt 3/4 plywood across it and cover with carpet. build your drive ons to suit yourself or buy them not too expensive. a lot of trailers down here set the plywood floor far enough forward to mount a couple rollers on very end of trailer to help in dry loading and also it helps with shallow launches where you don't want to get your rear brakes wet. like in salt water
    Last edited by bgmcl60; 06-27-2017 at 08:30 PM.

  5. #5
    Member Bart's Avatar
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    Re: Modifying a boat trailer for an airboat

    nice trailer to start out with, you are right it is a heavier trailer, but nothing wrong with that.
    brakes... i imagine that this trailer was able to hold a 2500 to 5000 lb boat. from looking at the axle and support it has. so if it had that heavy of a boat. it is just a safety measure to keep from pushing the tow vehicle into something if needing to brake real sudden, nothing like having the trailer jack knife on you.
    but it is mandatory for double axle trailer to have at least 1 axle with brakes. single axle trailers you can have brakes or not. the choice is yours

    as far as where to position your boat on the trailer. when you are all said and done, with the boat on the trailer you want to have around 200 lbs of tongue weight. for good towing. (this is what i have on all my trailers) most hitches are rated up to 500 lbs.
    to much tongue weight and it changes the suspension up to where it can mess with your steering.
    and not enough weight, and the trailer will bounce and can could actually pick up the rear of the tow vehicle and push it sideways under sudden braking or turning.

    on the easy loader trailer the cross members are designed to pivot as the boat is loaded and unloaded. so you may need to take that under consideration as you attache the bottom rails and build the bed for the airboat to ride on.
    if you make the cross members solid, this may transfer the twisting and sway energy to other parts of the trailer, which after time could create problems. after some time. these trailers are designed to flex as they go over bumps and are loaded and unloaded

    these are some of the thoughts that i have, about the few questions that you asked. but it looks like it should work good for your boat.
    Last edited by Bart; 06-27-2017 at 10:32 PM.

  6. #6

    Re: Modifying a boat trailer for an airboat

    I'm going to put a telescoping tongue in the back of the trailer not to pull with.
    To push it in to the muck and drive the boat off, That's the plan anyway

  7. #7
    Super Moderator Corky's Avatar
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    Re: Modifying a boat trailer for an airboat

    Thanks for the reply BGMCL60... And it's not just you thinking about pulling the brakes off this trailer...As cautious as I am with safety I just can't justify a need for those surge brakes hauling my mini around...It's just a bunch of problems where there doesn't need to be...The only drawback that I can see is the trailer is titled for the heavier load{calling for those brakes on the trailer} and might create a problem in that aspect...With that being said I've seen plenty of crazy,homemade air boat trailers on the road locally and nobody around here has ever raised an eyebrow at them...

    I found a standard coupler with a 5000lb rating and I think I'm going to use one of those that way it still exceeds the rating of the trailer..Pull the brake hardware in the hubs and move on with the fun stuff on this...

    Interesting idea on the flooring between the bunks to be honest I've never seen a trailer with the flooring/carpet between the bunks around here but it's a great feature and it would conform to a slight bottom arch..Not to mention spanning the weight distribution the best it can be...

    Now, onto the drive ons...I've been studying these and there seems to be two basic types..A series of rollers or an angled "ramp" with that roller you've pointed out at the break point...Here's a pic with an example of each...
    Attached Images Attached Images    
    Last edited by Corky; 06-27-2017 at 11:10 PM.

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  8. #8
    Super Moderator Corky's Avatar
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    Re: Modifying a boat trailer for an airboat

    Hi Bart, I've seen where the bunks are simply 2x4 or 2x6s and were on swivels also I'm guessing to conform as stuff moves around... I can't help but wonder with the relatively light airboat if there really would be much stress on the boat or trailer ???

    Yes, you're right about moving the load around for the perfect balance... I haul heavy equipment at work with a tractor/lowboy trailer{class A} but the real hair raising stuff is with the smaller trailers and heavy loads you need to get them just right or those symptoms you've described will take you for a ride !! You know, I wasn't even thinking in terms of weight distribution I need to take that into consideration...

    The GVWR load is rated for 4000 on this trailer that's why I want to use the heavier coupler {5000lbs} so there's no question about the rating even though I'll be hauling a 700lb boat !!! EDIT: I found a pic of the data tag I saved it in case it gets damaged...
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    Last edited by Corky; 06-27-2017 at 11:33 PM.

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  9. #9
    Super Moderator Corky's Avatar
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    Re: Modifying a boat trailer for an airboat

    Quote Originally Posted by Coyotes-R-Us View Post
    I'm going to put a telescoping tongue in the back of the trailer not to pull with.
    To push it in to the muck and drive the boat off, That's the plan anyway
    That will be pretty slick when you get that engineered...It will certainly open up the options for getting your boat in and out of any terrain or conditions...

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  10. #10
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    Re: Modifying a boat trailer for an airboat

    Tongue weight is the most important. You want to have enough weight on the tongue so you don't hear all that bouncing back there on the ball. I'd set it up for what it needs. I like the back of the transom even with the back of the trailer, the rudders sticking out never bothered me. I have all rollers on mine and If I had it to do over I'd use rollers and bunks. With all rollers it just slides off too easy, I can't do the back up and brake launch when the water is too low to take it off normally. On my uncles trailer I just put in cross braces where I need them for the rollers and the bunks. That trailer is a great one for loading and unloading. My uncle even commented that the trailer was the best part of the build.

    Also take into consideration where you will be launching from most of the time. The angle of the trailer in reference to the trailer. My trailer sits high also because I used a trailer like yours just not as heavy. Look at it and see if there is anything that the boat will hit when loading or unloading when at the angle you are at when launching. I hate it when I go to push the boat off at a steeper angle and the boat gets hung up on the back crossmember and I have to crawl out on the trailer to push it off. I'd also put a walkboard on it, take that into consideration when you're deciding where you need to put your cross bracing.
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  11. #11
    Member Bart's Avatar
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    Re: Modifying a boat trailer for an airboat

    thanks for posting those pictures of a few different trailers with their drive on ramps. it has given me a few ideas. i don't know if i will ever have something that fancy,
    but it is fun to see the craftsmanship you have in doing your own work, and nothing you have done is second rate.
    i knew that you had operated heavy equipment, and been around the block. i have a class a also. but i felt like putting those thoughts out there, for others to read and think about.
    we all see just a little entertainment sooner or later. sometimes it is our own doing, but many times it is dealing with shortcuts that others take, in our travels.

  12. #12
    Member aewrigh's Avatar
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    Re: Modifying a boat trailer for an airboat

    When I bought my hull I used a 1970-something bass boat trailer and modified it to fit the boat. Since then, I came up with a double jet ski trailer that I just started modifying. I will post pics on my build page when time allows. It is super wide and may look a little goofy but I will have 16" wide walkways down both sides to facilitate loading/unloading when I need them. I am using treated 2x6's for the side guides and treated 2x8's for the bottom bunks.

  13. #13
    Super Moderator Corky's Avatar
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    Re: Modifying a boat trailer for an airboat

    Thanks guys all good info here..I was looking for a double jet ski trailer originally but there just wasn't any that I found at a reasonable price at the time...So I got what I got... I've been thinking as I remove the brake system about what mods I want to do...As usual I'm on overload with thoughts...

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  14. #14
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    Re: Modifying a boat trailer for an airboat

    Corky,
    In my opinion less is more on your trailer. Loose the brakes, you won't need them. I used 2"x6" carpeted rails and the boat cradles nicely and slides easily with the slick bottom. As far as the back end is concerned, You probably don't need a transition as long as the 2"x6"s extend just back of the metal cross beam. I've loaded mine easily from any angle. The back of my boat hull rides flush with the back of the trailer and the rudders stick out behind but that's not a problem as no one wants a sharp rudder through their windshield so they stop well back. I did add a set of padded vertical guides at the back to aid in keeping the boat straight during loading and erratic highway maneuvers.
    11'6" Marty Bray Hull
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  15. #15
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    Re: Modifying a boat trailer for an airboat

    I put my rollers in the rear and the bunks in the front so when I pushed the boat off it was lifted off the bunks and rolled off on the rollers. With the rollers in the back it makes it much easier to load, the boat hits the back roller first. It helps when driving it on also, it;s easier to drive it on then once you get on the bunks it keeps it from sliding off.
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  16. #16
    Super Moderator Corky's Avatar
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    Re: Modifying a boat trailer for an airboat

    So the brake system is history...I pulled the surge coupler, all the hard lines running through the frame, and the brake hardware in the drums...So now I have basically a roller axle with no hardware between the backing plates and drums to create any drama down the road...

    Here's what concerns me..Being a heavier trailer the 6 lug load range D tires sit higher than the standard 5 lug tire..The river here is relatively shallow here{3-4ft possibly even less} at the house and most areas within miles of here...I'm leaning hard on adding those back ramps to the trailer so I can be assured I can pull this boat at any ramp on the river... I'll get a measurement of the frame rail height and the cross member height this weekend so we can determine if I'm overthinking this...

    Next up....I really like the idea of adding a strip of carpeted plywood between/on the 2x6 rails...Why ? Because I could walk on it to fasten/grab the boat if need be..This trailer is LONG and having the ability to be on there in the water is a big plus as far as I can see...I don't see how spanning the load across that carpeted center instead of just the rails would hurt launching the boat with the slick bottom or am I thinking wrong ???

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  17. #17
    Administrator Papee's Avatar
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    Re: Modifying a boat trailer for an airboat

    I have the same deal Corky, my trailer doesn't even know the boat is there. I haven't had any problems though with the height. I have had times where it was low and all I could do is pull the boat up to the back at the bow arch and hold it there until I could get the winch rope hooked up. I have my walk board lower than the rollers but on my trailer I have the old paper rollers that go from one side to the other not front to back. This also helps for loading because I'm against the back roller when I pull up. I always load mine by hand, no drive on. I find it easier, I just pull in up stream then back the trailer in. I just push the boat out holding the mooring rope and let it float to the trailer then pull it on.
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    Re: Modifying a boat trailer for an airboat

    Here are a couple pics of my trailer. I have since decided to use composite deck boards instead of treated lumber for my boards.
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  19. #19
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    Re: Modifying a boat trailer for an airboat

    I know it is overkill but I tend to do that lol. I added three 3x3 runners , 1/4" thick heavy wall 2x2 tubing for my uprights, capped them off and added a piece of 3" c-channel between them to support the deck board. I also cut off the bow support I had built for my old trailer and added it to this one. Just got through painting it this evening. I also had to weld up about 30 holes and grind off stuff from when it was a wave runner trailer.

  20. #20
    Member Bart's Avatar
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    Re: Modifying a boat trailer for an airboat

    Aewrigh, you will like the composite deck boards. when i first took mine out for the trial run, i had treated lumber, the boat wouldn't slide off for nothing. but now with gator glide and a couple of composite boards on top of the treated lumber. it will slide off the trailer with a gust of wind, if it isn't tied down.

    Corky, an other question, on my snowmobile trailers i have a what we refer to as a salt guard. on the front of the trailers. to protect the sleds from rock chips and and dirt that gets kicked up from the truck tires.
    i haven't seen many boat trailers with a shield on the front of the trailer. I would hate to see your paint get chipped from truck tires kicking up any rocks. ( just thinking out loud) but then most people don't trailer their boats around during the winter.

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