Bimini Sways a lot. Ideas to stabilize it

[64osby]

1973 Starcraft 21' Mariner Center Console with a factory original Bimini top in great shape. Trying to find a way to stabilize it so it can be used more. At speeds above 15 turns, wakes, and waves get it rocking side to side quite a bit, 12" or more at the top.

Any ideas are welcome.

Here is the top.

It is attached to a slide for the main attachment, back for storage, forward when deployed.

The top tube in the pic above is the front support, it snaps off and mounts to the inner gunwale with a thumb screw fitting.

The back straps attach with clips to these.

At the front of each slide there is a bracket. I have no idea what this is for but I wonder if these could have been a mount for a sway tube possibly

I use the bracket with the rope shown to hold the bimini slide forward when the top is up but not deployed.

My first thoughts are to use straps from the top outward to the gunwale, maybe find a way to clip to the rub rail or outer gunwale angle. Second is to have straps that mount to the front center of the console, don't like the idea of blocking vision though.

Being a center console makes getting any strap or tube inward to provide a good angle hard as it will interfere with walk space and I am tall 6' 4".

Also hoping the solution would work for the upright stored and deployed positions.

Any brilliant ideas out there.

 

[Bob's Garage]

Re: Bimini Sways a lot. Ideas to stabilize it

If I was to guess I would say that physics is working against you. The top is still going in one direction when you suddenly turn to another, then it has to complete it's swing and then follow you on the new tack. In short order it becomes a pendulum which could eventually destroy itself in a dramatic manner.

To my mind there are 2 remedies;

1) Lower the top until you are thru with the activity causing the rapid oscillation of the top.
2) Install a 1/2 tower or t-top, which are permanently affixed to your boat. This would be heavier and more cumbersome for a small boat.

 

[Mischief Managed]

Re: Bimini Sways a lot. Ideas to stabilize it

 

[Fireman431]

Re: Bimini Sways a lot. Ideas to stabilize it

Add 2 struts to the frame work.

 

[Scott Danforth]

Re: Bimini Sways a lot. Ideas to stabilize it

my bimini has two straps coming from the center at 45 degrees to prevent swaying.

 

[DeepV]

Re: Bimini Sways a lot. Ideas to stabilize it

I regularly run 40 mph in my Lowe FS 175 with the bimini top up. It doesn't move much at all. You may try keeping the leading edge a little higher than the back. If the front is higher the wind seems to stabilize it some as it passes underneath.

The top is a regular 6 foot 3 bow from Cabelas mounted on sliders with straps fore and aft on either side. Keep the straps tight too.

 

[64osby]

Re: Bimini Sways a lot. Ideas to stabilize it

To my mind there are 2 remedies;

1) Lower the top until you are thru with the activity causing the rapid oscillation of the top.
2) Install a 1/2 tower or t-top, which are permanently affixed to your boat....

We do have it down most of the time, trying to find a way to have it up and not self destruct. Don't want a tower or a T.

Mischief - Your support looks great, no where to mount one on my center console

Add 2 struts to the frame work.

Fireman - I think this is a good idea but the angle and attachment points are the real question. Makes me wonder if mounts that are 5 or 6" farther out will really make a difference.

my bimini has two straps coming from the center at 45 degrees to prevent swaying.

This would be great but would cut off the walking space.

I regularly run 40 mph in my Lowe FS 175 with the bimini top up. It doesn't move much at all. You may try keeping the leading edge a little higher than the back. If the front is higher the wind seems to stabilize it some as it passes underneath.

The top is a regular 6 foot 3 bow from Cabelas mounted on sliders with straps fore and aft on either side. Keep the straps tight too.

As it is straight line travel is fine, it is the sway that's the problem. Straps could work but getting them in the right place is the concern.


Being a center console next to the gunwale are the walk paths. The whole boat is open under the bimini except for the center console.

Since all the attachment are now in a straight line on the inside of the gunwale. Wondering if the rear straps were moved out to the top outer edge of the gunwale, might give a little sway control to the rear of the bimini. Then maybe move the front mount to the top outer edge of the gunwale and find a 90 mount for it. The would pick up about 10" extra width at the front and rear attachments.

 

[spdracr39]

Re: Bimini Sways a lot. Ideas to stabilize it

I regularly run 40 mph in my Lowe FS 175 with the bimini top up. It doesn't move much at all. You may try keeping the leading edge a little higher than the back. If the front is higher the wind seems to stabilize it some as it passes underneath.

The top is a regular 6 foot 3 bow from Cabelas mounted on sliders with straps fore and aft on either side. Keep the straps tight too.

I agree it looks like the front is to low which allows the air to push down and cause it to be unstable. If you shorten the straps on the back and let the front up higher the air will catch under it and hold pressure on the top stabilizing it more. You can also put a few twists in the straps to keep them from vibrating and getting loose.

 

[Jlawsen]

Re: Bimini Sways a lot. Ideas to stabilize it

I agree with it being too far down in the front. It's trying act like a spoiler and there's excessive down force on the back. I had a boat once that I did nearly the same thing with and I broke the uprights coming around a turn in a narrow channel when the wind suddenly changed directions. That's when I figured out what I'd done wrong.

 

[theBrownskull]

Re: Bimini Sways a lot. Ideas to stabilize it

I would leave the original frame alone and add additional straps. They are easy to sew on and cheap to buy; most upholstery shops carry them. And if they don't work you can take them off. Or take it to an upholstery shop and show them the problem and they can sew the straps on for you.

 

[64osby]

Re: Bimini Sways a lot. Ideas to stabilize it

I agree it looks like the front is to low which allows the air to push down and cause it to be unstable. If you shorten the straps on the back and let the front up higher the air will catch under it and hold pressure on the top stabilizing it more. You can also put a few twists in the straps to keep them from vibrating and getting loose.

I agree with it being too far down in the front. It's trying act like a spoiler and there's excessive down force on the back. I had a boat once that I did nearly the same thing with and I broke the uprights coming around a turn in a narrow channel when the wind suddenly changed directions. That's when I figured out what I'd done wrong.

Thanks for chiming in guys. This is 39 year old technology and the front support is not adjustable. The only way to lift the front is to move the front support up on the gunwale.

You all are making me think (hard sometimes). I'll try and see if there is a way to mount the front supports on the gunwale, it will also get the front supports outward a little which might also help with the sway. Every mount won't be in line like that.

 

[rivermouse]

Re: Bimini Sways a lot. Ideas to stabilize it

From the picture it looks like the angle of the canvas in the rear needs to be extended on each side by a foot. This will help the side sway.It would help also to drop the rear frame by 5 or 6 inches to give it a lower center of gravity. Do this and I promise you will see a big improvement.

 

[64osby]

Re: Bimini Sways a lot. Ideas to stabilize it

I would leave the original frame alone and add additional straps. They are easy to sew on and cheap to buy; most upholstery shops carry them. And if they don't work you can take them off. Or take it to an upholstery shop and show them the problem and they can sew the straps on for you.

Brownskull - I was posting when you replied, yea it took a long time for me. Added straps will be my second fix if the first doesn't work. Thanks for looking.

 

[64osby]

Re: Bimini Sways a lot. Ideas to stabilize it

From the picture it looks like the angle of the canvas in the rear needs to be extended on each side by a foot. This will help the side sway.It would help also to drop the rear frame by 5 or 6 inches to give it a lower center of gravity. Do this and I promise you will see a big improvement.

I can move the rear attachments and will look at that. The frame won't drop unless it is cut, not going there yet. Also being 6'4' tall I want it as high as possible.

 

[snowman48047]

Re: Bimini Sways a lot. Ideas to stabilize it

Your 5th pic, of the little bracket in front of the slide, is a mount for a "down east" style rod holder. Don't have any ideas for the top.

 

[64osby]

Re: Bimini Sways a lot. Ideas to stabilize it

Your 5th pic, of the little bracket in front of the slide, is a mount for a "down east" style rod holder. Don't have any ideas for the top.

Thanks snowman, good info, I had a feeling someone here would know.

 

[Expidia]

Re: Bimini Sways a lot. Ideas to stabilize it

Looks to be a similar bimini to mine 3 bow etc. Mine is tight with no sway at all speeds and on a similar small aluminum boat. I would experiment a little with adding two more straps as others have suggested. Seems to me your issue might be that the straps are built into the bimini are not forward or aft enough. To prove this take some cord and tie it high onto the frame. Wrap some plastic electrical tape around the cord looped around the frame so it won't slide down. Then go out with a buddy driving while you hold the other end taut about a foot back from where the straps are attached now. Then try the same thing with the forward straps and see if either new position eliminates the sway. Bimini straps need to be quite tight. Sometimes tight one sing in the wind. Just unhook and put in a twist or two, no more singing.

You could also bring your rig to a good local canvas shop for their opinion. I had a custom enclosure made by a local shop and was amazed at the work they were doing on some other boats in the shop. I think they will point out to you that the supporting straps especially in the rear are not attached far enough back. A shop could lengthen or replace your straps for cheaper than replacing the top when your frame finally snaps from the sway stress. I broke one by just "touching" a piling! These aluminum frames snap like a twig. Don't let anyone support themselves while getting into your boat by holding onto the frame or someone who helps you into the dock space by grabbing the frame and pulling the boat in!
Longer straps are cheap online. A rivet kit with installer tool is like $10 at Harbor Freight if you want to do it yourself and have to take some of the frame apart if it's rivieted. But in looking at your rear straps which appear to be built into the bimini a canvas shop can replace or lengthen them for you. You or they can add strap hooks if need be on the top of the gunnels or inside. It's only two real small screws that hold them on. But you first need to assess if longer straps would work. Dont mount on the top if you have a tight fitting trailering type cover.

But try the mock repositioning of the straps first while the boat is moving to see if that will solve your sway.

 

[64osby]

Re: Bimini Sways a lot. Ideas to stabilize it

Took the boat on vacation last week and the Bimini worked great.

I made a couple of brackets and moved the front attachments off the side of the gunwale to the top of it, about 4" up and out about 3". This raised the front and lowered the back, the rear straps were adjusted and very tight.

I also used a couple of HD bungee cords off the front to the bow rail. This helped stabilize the top in the open and closed position.

Here we are grilling at a sand bar off one of the islands on the lake. Very nice to have some shade on those hot days.

Didn't do any WOT runs with it up but it worked great at 32mph and below.

The Bimini and the Dodger covers were also very nice when fishing in the rain.

The front Dodger cover also worked great on the cooler days, the kids would sit under it while we were cruising around.

Thanks for everyone's input and help getting the Bimini stable.