Trailer bunks

[Chad]

So hows about some content, to get this place started?

Where'd you put your transverse bunks in relation to the boat, and where does your keel sit in relation to the trailer axle, fore and aft?

I'm think bunks under f53 and f169, and centering the keel about a foot in front of the axle to ensure some tongue weight. But I could move the bunk aft to f89, to provide a wider support, but this might make the bow/knuckle a little more vulnerable at steep ramps.

What have yous all found to work or not work?

[slowpoke]

And how many bunks? It seems to me everyone is using just 2 transverse bunks; Is anyone using for and aft runners/skids?

[Kevin]

My bunks are at frames 53 and 169. They are 5" wide strips of 1/4" ply scraps that I laid on top of the fair hull and then did a fillet to the a piece of decent 3/4" plywood. I then used some grippy stair tread stuff that does not let the boat move easily. It's supposed to be great at getting the water way from the paint so you don't blister. The bunks are then bolted to the trailer frame in the appropriate spots.

Ron's bunks are just 3/4" plywood with some delrin pads that the boat rests upon. I was surprised at how he did it, but he said he hasn't had any problems.

You will want a nice wide opening in the back bunk for your keel bulb to glide through unless you have a really steep boat launch. I think Jeff's is like 15" wide with wing guides on the center opening to help center the boat as it comes onto the trailer. I retrofitted mine with a slot after the first disastrous launch. It's not as wide or as well executed as Jeff's. That's one of those to-do items that hasn't been gotten too. Maybe I'll do that next weekend. I can hang the back of the boat from the rafters and remove the rear bunk. And I'll be playing with epoxy for my rudder (finally).

I also have a bow roller which I would recommend. The boat doesn't touch it at all when it's pulled out, but while on the launch it comes into play and keeps the bow from hitting the trailer.

Also for the record, I think my trailer is about a small as anyone would want to go. 1200lb capacity. A 16' or 18' trailer would probably be a better choice.

Cheers, Kevin.

[Chad]

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Looks like the Midwest Three have their bunks at f89 and f169.

And I'm checking out how to load pics here.

[Kevin]

That's what I get for not going out and looking. I certainly haven't moved mine so front is at 89. I may move my bow roller aft a foot and see if that helps with retrieval. A longer trailer would also mean I wouldn't put the tail pipe in the water. But then it wouldn't fit in the garage so it's a trade off.

Kevin.

p.s. the pictures have scroll bars instead of auto sizing. We'll have to look into that setup.

[jray]

I just have to ask, why is everyone going with transverse bunks? Just wondering if there is something I've missed along the way. I know that Andrew went that way, are we all just following his example. I'm bringing this up as I am right at the desision point with my trailer. My counter is if flexable bunks running with the hull having even contact, and guides on the sides, would they work the same. Thanks for your thoughts.

[Chad]

Everybody's got structure running side to side. Some folks have stringers running fore and aft, but not necessarily where you'd place trailer bunks. If you use "flexible" fore and aft bunks, they still need their points of support to be where the frames are, or the flexible bunks will push into the hull panels. Ben used a transverse bunk about a foot in front of F169 and it was noticeably indenting the hull there (he plans to address it soon). The 1/4" ply skins just aren't stiff enough mid-panel to support the boat.

If you had stiff lengthwise bunks carefully shaped to fit the hull, they would still only be providing support at their intersections with the frames, resulting in much higher point loading.

Transverse trailer or cradle bunks are common in many boats with transverse frames/ring frames, and moderately or very flexible hull panels. Probably easier to build, too.

My trailer, picking it up tomorrow:

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I'm making bunks now, and I'll need to strip all the power boat style stuff off that's on there now. It has an interesting tilt feature, not sure how useful it will be- maybe most useful for dragging the boat onto the trailer from my front yard!

And since I started this way before I asked here, I'll go ahead and put the forward bunk at f53 and see how it works.

[Mist]

Though I’m a long way from putting my boat on a trailer I’ve already put a lot of thought into it. Hauling the boat down the interstate with it bouncing along on a trailer is probably the harshest environment the boat will be in. The shock loads will be high. I think it’s best to distribute the upward shock loads from a bump in the road over the largest supported area possible. For the i550 I believe transverse bunks under frames 169 and 89 are best. Additionally, the keel bulb should be supported with an independent bunk. I’m choosing frame 89 because it’s wider than 53 and has more surface area to support the loads and also the compression post for the mast is right there allowing shock forces to be distributed through more of the boat’s structure.

[Kevin]

I use a nylon hold down strap with to hold the boat to the trailer so it doesn't bounce our move on the trailer. With the grippy rubber on the bunks plus the strap the trailer and boat move as a unit for the most part. I had no issue cruising up to Madison last September. One trick is to make sure your tires are at the proper pressure because an under inflated tire is a bouncy tire.

Here's a picture of my trailer stripped of all the powerboat junk that came on it. The rear bar swings and had rollers on it. I ended up having to have it' welded to the frame so that the aft bunk didn't rotate down.

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p.s. I turned on "thumbnails" so now images will automatically resize in the post using a thumbnail. If you click on the image you'll see the full sized image. You have a 25MB quota for attachments so use them wisely .

[Kevin]

Ok, here's a fun picture I just found. Bottom of the boat is primed and sanded out. Yes I added pigment to the primer so I could see when I was sanding through a layer. I have lots of blue pigment left if anyone is interested, but I digress. Between the hull and the bunk is the rubber tread that I planned to use so the sides would be properly positioned and the curves would be right.
Later.

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[jeff.dalsin]

One other thought on trailers...

It is possible that the trailer that any of us acquires will be spec'ed for a heavier boat and will be equipped with springs that are too stiff for our light wieght rocketships. A stiffer ride could put extra stress on the boat.

Just something to keep in mind!

Jeff

[Chad]

(pic)

Using an upside down boat for the bunk mold was certainly my original plan, but that's not gonna happen for me at the moment. I need the bunks now, and the boat isn't ready to flip. I'm building then to the plan, bevelled fore and aft as needed, adjusted for the added thickness of hull skins and a yoga pad, and eyeball checked against the hull. Should be fine...

A stiffer ride could put extra stress on the boat.

Yup, my trailer's rating is 2100# and my boat's first travels will be while unballasted, so it will get bounced more than usual. I'll knock the tire psi down a bit to help- 55psi is pretty brutal.