Cobia tower / new top on a 306 Bimini - anyone done it?

[Xavier]

Hello all,

I own a 1999 306 Bimini and I am looking into a full top replacement that would include a cobia tower, and I would be very glad to hear from anyone who has been down this road on a 306.

A bit of context, because it drives the whole problem: the boat lives in Conakry, Guinea, in West Africa. I fish offshore for blue marlin and sailfish. What I am after is height - a standing position above the top so I can watch the trolling lines and spot fish well behind the boat. I do not need a full second helm. Steering alone at the top would be plenty; engine controls up there are not a requirement, and I would be happy to handle throttle from the lower helm or add a wireless autopilot remote.

What I would like to know:

1. Has anyone here put a tower, or a new top with an integrated cobia tower, on a 306 Bimini or a Canyon 306? Photos would be worth a lot to me.

2. Does the factory hardtop work as the floor of the upper station on this hull, the way marlin towers usually do, or does the top have to be replaced or reinforced first?

3. Which shop did the work, and what did it run? I have written to Atlantic Towers and to Bright Light Welding to ask, but first-hand experience beats a brochure.

4. The hard part: the boat cannot come to a US yard. Has anyone had a top or a tower built from measurements and photographs, shipped as a kit, and assembled and welded locally? If there is a measuring procedure or a template that makes this reliable, I will follow it to the letter.

5. Anything I should know before committing - deck attachment points on this hull, added windage, effect on stability or on the ride?

Many thanks for any pointers.

Xavier

 

[DennisG01]

Right up front, I have not done this modification.

While "physics works", you're not going to adding THAT much weight compared to the boat's dimensions that it would be a major concern. I highly doubt you'd notice anything... or very, very minor... when no one is up there. When you and another guy are up there Im sure you will notice a difference in some cases with the amount of boat rock - but since your weight is relatively centered, it won't impact the boat as much. As I said, I haven't done this specific mod - but just going off of years of other projects and being on/around boats my whole life, I think you'll be just fine from the "extra weight" standpoint.

Now... could you use the existing top as your new "floor"? The aluminum structure is MORE than capable of handling this. Concerning the actual top... correct me if I'm wrong, but in your boat it's a beefy structure of reinforced fiberglass? Again, that should be fine - but get on up there and walk around - don't be gentle - walk hard. Going with that assumption...

Now, the fun part... the "thinking/ideas"...

First thought...

-- Fashion an aluminum structure (tubing) that goes around the perimeter of the top. Think of something like the brass bar used a footstep at a bar in a restaurant. Let's call this the "base". To attach it to the top, fashion short, vertical legs (same aluminum tubing) in a numerous places (maybe 6" high). These would be welded to the base. At the bottom of these legs would be 1/4" plates that are maybe 8" long. These would then get thru-bolted to the top (with the same size plate being used as a backer plate .

-- You know have something that you can build upon AND you have significantly increased the rigidity of the existing top.

There must be aluminum welders somewhere around you - search around - I'd bet you can find someone that's being welding their whole life - maybe just working out of their house. But you'll know how good they are once you look at their work (look at the welds). I think the cost of getting something fabricated here in the States, shipping it, then STILL having to weld it together is not the way to go. Plus... what if it's not quite right?

As I'm writing.. I just remembered that there's a nice guy on here that did something similar to his Grady - I believe it was a 22-footer. I think he said he was very happy with it and it didn't alter the performance much. His name is Luckydude - reach out to him or search for his thread on this.

 

[Xavier]

Thanks Dennis, that is genuinely useful. Let me correct one thing straight away, because it changes your first idea.
My top is not reinforced fiberglass. On this boat it is a canvas top on a tubular aluminium frame. Grady-White confirmed to me last week that a 1999 306 Bimini left the factory that way - a soft top on tubes, not a rigid hardtop. Mine is the original structure, re-welded in one spot and reinforced in several, and it shows no weakness today. Measured width: 2.20 m, about 7'3". Photo attached.
So "use the existing top as the floor" is off the table as it stands, and that leaves me with two questions.
1. Is there a sensible way to work out whether that aluminium frame could carry a person standing on it? What would I need to measure - tube outside diameter and wall thickness, span between legs, how the legs land on the deck? I would rather calculate it than find out the hard way.
2. Or is the right answer simply that a cobia tower should not touch the top at all - legs down to the deck and the console, straddling the existing top? That is what I understand the usual architecture to be, and it would make the strength of the top irrelevant.
On fabricating locally rather than shipping a kit: point taken, and you are probably right. One caveat on my side - I have good stainless welders available here, but aluminium is a different trade and I do not yet know what I can find in Conakry. Worth noting too that welding onto 6061-T6 drops the yield strength in the heat affected zone by roughly half, and it does not come back without heat treatment. So if anything gets reinforced, I would want it bolted with backing plates the way you describe, rather than welded onto the existing frame.
I will try to reach Luckydude. Thanks again.
Xavier