Mounting bunks for a narrow trailer

[ba_fisher]

Got myself a trailer!

I think it’s a Shoreland’r jet ski trailer from the 80s. It’s a bit narrow. The widest part of the frame is just 41 inches, which is narrower than the width of the narrowest points between the tubes of my True Kit 330 catamaran.

I want to put two flat bunks (6 or 8 ft long?) where my tubes will sit on. Any suggestions for how to mount them?

[ba_fisher]

Most of the brackets are of this type, which is usually mounted on cross members. But I don't have enough width, especially for the front cross member.




I found these, which look perfect for mounting on the two sides of the trailer (in front and after the wheel fenders), but they are darn expensive!



One option is to extend the width of the trailer using "super structs" from Home Depot so I can use the first type of brackets, but I am wondering if there are other alternatives (hopefully better both mechanically and aesthetically)

[Peter_C]

Do you plan to dip the trailer into salt water? Are you planning to leave the outboard on while trailering?

What size outboard is your boat using? Weight of said outboard? What does the owners manual say about towing with the outboard on?

Might be good to make the trailer a flat bed with plywood and just strap the boat down. The owners manual should have something in it regarding trailering. Instead of dipping the trailer I would use a nice set of transom wheels even in fresh water. Beachmasters are pretty awesome.

[chipko]

For a catamaran I’d recommend raised bunks positioned to support the floor directly adjacent and hard up to the tubes. For a 330 TrueKit I’d hazard the bunk spacing will be somewhere between 26” to 30” so trailer frame at 41” plenty wide enough. Bunk supports could possibly either be directly off frame or secondary cross beams.

[ba_fisher]

Originally Posted by chipko

For a catamaran I’d recommend raised bunks positioned to support the floor directly adjacent and hard up to the tubes.

My boat is an air floor. Will it be strong enough to bear the weight of the tubes?

Also, while the tubes are connected by the transom at the rear, the bow is held together only by the piece of fabric underneath the air floor. I worry that the bunks will be pushing the tubes apart and ripping that piece of fabric away.

[ba_fisher]

Originally Posted by Peter_C

Do you plan to dip the trailer into salt water? Are you planning to leave the outboard on while trailering?

What size outboard is your boat using? Weight of said outboard? What does the owners manual say about towing with the outboard on?

Might be good to make the trailer a flat bed with plywood and just strap the boat down. The owners manual should have something in it regarding trailering. Instead of dipping the trailer I would use a nice set of transom wheels even in fresh water. Beachmasters are pretty awesome.

I would prefer to dip the trailer in salt water, but I also have launching wheels so I can hand-launch as well.

The boat is very light and the trailer is rated for over 1000lb. When I towed the trailer home by itself, it bounced really bad. My outboard is only a Suzuki 6hp (54lb) so I will leave it inside the trunk. True Kit also recommends against towing with the outboard.

Since the trailer has 4 round corners, I am thinking of using the first type of the brackets that I mentioned in post #2 -- put them at 45 degrees at the 4 corners, and mount 2 wide bunks horizontally. This will essentially make it a flat bed as far as the tubes are concerned.

Maybe I'll add two rollers at the end of the bunks to make it easier to load/unload the boat.

How tall should I mount the bunks above the wheel fenders? I am thinking of using shorter brackets and mount the bunks just above the fenders, so it's easier to take the boat on and off the trailer. However, I've seen people who mount their bunks really high. Is there any reason for doing so?

[Steve509926]

Hi ba,

My take on adding bunks to a trailer, albeit a wider trailer than you have bought.

https://www.rib.net/forum/f49/carava...ler-86495.html

The upright stanchions are 41mm SS Slotted U Section
https://directchannel.uk.com/41mm-sl...BoCGoYQAvD_BwE

I have changed the trailer slightly since I took those pictures. Front stanchions are a bit higher, the back ones are a bit lower and the bunks now have an HDPE cover on them - just makes it easier to launch and recover the SIB.
I launch in fresh and salt water, wash well after each use. I have also made sure the bearings are well packed with grease.

[Peter_C]

That trailer will get destroyed very quickly in salt water. The wheels will rust causing an air leak from the tires. I often launch at Horseshoe Cove under the Golden Gate Bridge where the surge can come right up to the back of my minivan and I have a VERY long trailer tongue, as it is not the correct trailer for my current RIB, but the side benefit is my vehicle is further from the waterline. Most launch sites on the Bay are not as surgy, especially deeper in the Bay. Breakwater in Monterey is known to kiss vehicles with salt water which is really not good.

When I had a Zodiac SIB it weighed about 500lbs ready to go in the water. I could hand launch solo but it took two folks to recover it after removing extra weight like the electronics tower @33lbs, fuel tank @10-40lbs, along with the anchor and rode @35lbs. Getting it on and off the trailer was not a big deal. Lift the bow and wiggle side to side pushing it back a few inches at a time. Once the boat could be pushed bow in the air so the transom wheels could roll it was off to the water. Reverse procedure for putting it back on the trailer, but I used the winch to put it back on the trailer for the last little bit. Once I built transom wheels for it I never dipped the trailer in the water ever again. Trailer wheel bearings don't fail often when they are not submerged.

If it were me I would build some kind of mount to store the outboard on the trailer simply because I hate smelling gasoline, and wouldn't want it inside my vehicle. Maybe under the bow on it's side, using a couple blocks of wood to keep the shaft from moving and then clamp it to a 2x8" or some plywood. Then find a place to mount the external fuel tank too.

I would start by blowing the boat up and setting it on top of the trailer to see how it sits.

You can probably lower the tire pressure some so the trailer doesn't bounce as much. The more weight added to the trailer the better. Tongue weight should be around 15% of the trailer weight. IE: 200lb trailer should have 30lbs of tongue weight. You can move the axle around as needed to achieve that goal. Speaking of which I have never seen a single u-bolt setup for holding the springs to the axles.

As to the height of the trailer, as low as possible. I call the towers that hold bunks stanchions, right or wrong. They can be easily built out of aluminum or other metals even without welding, by using angle metal with holes drilled for bolting. U-bolts could hold the stanchions to the trailer. Bunks are just pressure treated wood with carpet over them. Better is something like Trex, or even better is a slippery plastic material with no carpet. I don't see any benefit in using bunks vs a flat sheet of plywood though if you plan to support it under the tubes. Looking at photos it seems your boat sits really nice and flat. The trailer could have some L-track or T-track mounted to the sides so you can strap over the top of loads. S-hooks when they come loose fall off. Clipped on hooks/latches do not. With plywood on top the trailer could be used for hauling other things too. (I have a cheesy 4x8' Harbor Freight trailer I couldn't live without.)

[ba_fisher]

I am warming up to the idea of converting this into a flat bed. Found a picture on the net that I liked:



This way I can also use the trailer to haul stuff from Home Depot.

The wheel fenders are just 3 inches above the frame. If I place 2x6 pressure treated boards directly on top of the frame, the side of my tubes should clear the fenders.

I don't want to drill onto the frame, so I probably will cut some u bolts to the right length and counter-sink the wood so that the nut will be flushed. The u-bolts are about $10 a piece so if I cover the whole thing with 7 boards, I need to spend ~$150 on u-bolts! Are there any cheaper alternatives?

[ba_fisher]

Originally Posted by Steve509926

I have changed the trailer slightly since I took those pictures. Front stanchions are a bit higher, the back ones are a bit lower and the bunks now have an HDPE cover on them - just makes it easier to launch and recover the SIB.
I launch in fresh and salt water, wash well after each use. I have also made sure the bearings are well packed with grease.

Steve, I've been following your thread. What are your bunks made of? They look like two pieces of wood (or plastic planks) mated in a T shape.

[Steve509926]

Hi ba, 3x2 and 4x2 pressure treated PAR, screwed and dowelled to make an offset T. I then bolted them to the stanchions with SS coach bolts.
Sounds like u-bolts are just as expensive where you are as they are here!
You could reduce the number of u-bolts you need by joining the 7 lengths of 6x2 together with a couple of cross members. You would then only need 6 u-bolts to join it to the frame.
But, why are you using 6x2? Would it not be easier, quicker, cheaper and much lighter to use a sheet of 18mm ply?

[ba_fisher]

Originally Posted by Steve509926

Sounds like u-bolts are just as expensive where you are as they are here!
You could reduce the number of u-bolts you need by joining the 7 lengths of 6x2 together with a couple of cross members. You would then only need 6 u-bolts to join it to the frame.
But, why are you using 6x2? Would it not be easier, quicker, cheaper and much lighter to use a sheet of 18mm ply?

My frame area is pretty small (42" x 40" for the square part, 42" x 28" for the triangular part), so I feel like it won't provide enough support for a plywood sheet. Plus the plywood would look pretty ghetto :-)

[Peter_C]

Well I thought about it a little and one of the challenges to putting plywood on is going higher than the fenders right? Take the fenders off and flat deck with plywood. Since you won't be putting much of a load on the trailer you can lower the deck height some. There are plenty of holes already in the frame, and drilling in a new toy is half the fun. Some cost effective 90* brackets could be utilized to bolt a wooden frame to attach the plywood. Think simple. Function before form! Paint will make it look pro LOL

[ba_fisher]

I went to west marine today and found these brackets that have the right dimension for me.

https://www.westmarine.com/c-e-smith...010916351.html



This would allow me to mount a 2x8 bunk on top of each wheel fender. I'll probably leave just about an inch of space between the fender and the bottom of the bunk.

They seem pretty sturdy (1/4" galvanized steel). For safety, I can add one of these 45 degree brackets, in case someone steps on the bunks by mistake.

https://www.acehardware.com/departme...ectors/3407541



Will this work? I'll just attach two bunks and forget about making this into a flatbed.

Here are some photos of my boat sitting on the trailer





The following is a view from the ground up at the rear-left corner of the trailer.

[ba_fisher]

Yet another option is to u-bolt a unistruct vertically onto the frame, and use this T fitting to mount the bunks

https://www.amazon.com/Genuine-Unist...dp/B00O4FB91G/





Since it's almost 5.5 inches wide, should be good enough to mount a 2x8 on top.

This design seems to have better stability, and costs less, than the previous one.

[Peter_C]

Your design limits are endless. If it were me and I had to use bunks I would mount the bunk directly to the fender with a carriage bolt, along with angle brackets as that fender is decently strong itself, but 1/4" it is not. For the brackets I would find something that could be welded or bolted on (I made the ones for my previous Pacific trailer from TIG welded aluminum). You want the boat as low to the trailer as possible. Have you checked for carpet available in that width? Using a slippery plastic bunk say some kind of decking might be the best without carpet. Make sure you add a way to cross tie the transom and bow to the trailer. Release pressure when stored.

Cheap brackets can come in many forms. The trailer is not galvanized so painting the brackets is just fine. https://www.homedepot.com/p/Simpson-...T22Z/100375357

Drill a hole in the bottom, flip the bracket over and with two bolts to the trailer frame it will be plenty sturdy. Fear not drilling holes in the trailer. https://www.homedepot.com/p/Simpson-...HU28/100237519

https://www.homedepot.com/p/Everbilt...2044/315016280
https://www.homedepot.com/p/Everbilt...2474/315016356
https://www.amazon.com/YUMORE-Bracke...0BCPTTZX6?th=1
https://rightonbracket.com/product/h...shelf-bracket/

Good luck!

[ba_fisher]

Peter, thanks for the links!

The trailer is actually galvanized. It's just that the previous owner painted over it, probably due to partial corrosion. From what I can see, most of the zinc still seems to be there.

I found 18' x 18" carpets for about $40 on Amazon, which I can cut into two halves for both bunks.

I'll also put a keel roller on the end of both bunks to help loading the boat on and off.

[Peter_C]

You're over building and over spending. The boat is less than 100lbs so rollers will not be necessary. The boat gets tipped onto it's transom wheels like \ then pulled forward onto the trailer and dropped flat, and drug forward to the tie down point.

[Steve509926]

Originally Posted by ba_fisher

Yet another option is to u-bolt a unistruct vertically onto the frame, and use this T fitting to mount the bunks

https://www.amazon.com/Genuine-Unist...dp/B00O4FB91G/

Attachment 141843

Attachment 141844

Since it's almost 5.5 inches wide, should be good enough to mount a 2x8 on top.

This design seems to have better stability, and costs less, than the previous one.

Any particular reason why you are thinking of using 8x2?
4x2 is plenty wide enough.

[HDAV]

Check the axle position compared to the transom jetskis have a very different weight distribution to a SIB and OB so may it very nose light! Too light with motor raised ! And axle is not adjustable on that frame how much overhang behind the axle is there?