Fiber Glass Pontoon construction technique - Joining sections

Newbie here - Thank you for your great Forum!!

Background: I am designing a Pontoon boat 26'x10' (all fiberglass construction- molded components) to ship to Nome, AK for use on my Gold suction dredge. Reason to build and ship components is A) shipping costs expensive for metal pontoons B) can design a much more efficient working platform using FGM.

My Goal: 1) Fabricate standard pontoon sections U-shape 48"L X 32"W. 2) Glass together 6 sections in the field to form a single pontoon 24 ' total length.

My Question: What is the most structurally sound way to join the sections to form a single pontoon 24' length.

Note: finished pontoon will be stiffened along the top length by U -Channel Aluminum/ spray in expanding foam/ stringers (if necessary) glassed in place ?

Which method is strongest (see diagram) A) butt the sections together, and lay 3 or more layers?? 10 oz cloth and 2oz CSM OR B) make 2" flanges on the edges and bolt together the sections on the inside, then glass on the exterior. Is this option overkill? Are either of these options not recommended? Suggestions? Comments?

Thank you anybody for your help!!

 

Welcome to the Forum Michael.

Have you got a general arrangement drawing for the pontoon boat showing what the bow shape is like, and the method of connecting the two hulls together?
Is the deck area available sufficient for what you have to do when working?
Is there a possibility that you might want to dis-assemble the pontoon boat again at some stage in the future, or is this extremely unlikely?

Re the design, have you established what it's displacement will be at it's load draft while carrying the required payload?
Would some of this payload be movable, in the form of crew?
If so, have you considered the worst case scenario for stability, eg with all the crew on one side?

Re the method of attaching the hull modules together, I can see pros and cons for both methods that you mention.

 

There are pros and cons to both methods of joining the hulls.

But don't use the combination of glass you listed, that's a very weak laminate.

And if you were looking at a similar laminate for the hulls, don't.

 

A)Shipping costs will not change for pontoons, regardless of the material they are built off. For hulls that are comparable in strength, the weight is going to be comparable too. However, freight costs are going to be driven by volume, which should be about identical for the same load rating.
B)Can you define what "more efficient" means? Building custom hulls with fiberglass will be more expensive and time consuming.

 

You'd be better avoiding GRP for a gold dredge, too much abrasion and bumping the rocks and gravel. HDPE in a u-shape would be easy enough to fabricate from sheet materials, and stand up well to rough treatment.

 

Why would a steel barge not be superior ? Weld on site from flat sheets, plasma cut bits as needed ? Isnt it a bad idea to have open U shaped hulls when the main thing you are doing above deck is pumping a gazillion gals of water an hour which has the potential through a bit of a leak to fill the hulls and sink or capsize your raft ? If not steel then aluminum, but cleanliness and welding is quite a bit more challenging and more costly per lb.

 

Pay close attention to ondarvr. Your laminate plan is insufficient for a workboat, by a LONG way.

The u shape is confusing me as well. Grp in that shape sinks straight to the bottom if water gets in. Not what I'd call a pontoon.

And making the entire thing from grp is spendy and not gonna take shore well. If you never go ashore; fine. Bonding the sections together depends on loads. It is out of my wheelhouse to help you. I just know what you said is way too weak for even a pleasure boat.

 

Nome Alaska where the ocean is frozen for more than half the year ????? Launching and retrieval is going to be a significant part of operation, usually ice floes in the water on both occasions....

 

Glass over joints should be at least equal to laminate schedule of sections, maybe even more.
I’m partial to steel for heavy utility barges too, if it needs to be catamaran, just weld up long boxes for the hulls, slope one Or both ends up if it gets towed much.

 

You could ship all the steel parts pre-cut. A portable welder and construction tools fit in the back of a pickup.

 

Thank you, Sir for your reply. To answer your questions. The arrangement is like a typical aluminum pontooon bpat 8'X24'. Aluminum Pontoons with AL angle cross bracing, plywood deck. Will dis assemble in future. Total displacement 4,000 lbs max. Buoyancy 10,000 lbs. Pontoons sealed on top, foam filled, and 55 gallon plastic barrels inside alternating sections for buoyancy if water. Max 3 crew. Very stable most mass concentrated at about 8 ft on centerline.Bow shape typical pontoon pointed end. Boat 10'X26'. Main thing is a couple respondents indicated wont be very strong. But I've seen many fiberglass boat constructions 4'X 10 or 12' length fiberglass only and they looked plenty strong. Am i missing smth??

 

Thank you, Sir for your reply. Can you suggest a suitable laminate combo. Boat is 10'X26', Al angle stiffeners, typical pontoon boat construction. I've seen a number of glass only boats like a skiff, long and thin. Looked strong. What type of layup can you suggest to be strong? length wise especially?

 

Thank you

thank you Gonzo for your reply, Im a zero experience welder, but learn fast. Assuming that is the case, what is your suggestion for parts pre cut shipped and welded? thickness , etc. Just a off the top of your head cost est to build two pontoons 33-36" X 26'? Enough to make a min 10,000lbs buoyancy displacement.

 

Thank you for response sir. Basically, it is a medium utility operation. Not big commercial deal. Total weight equipment crew etc. Max 4,000 lbs. I need mobility and low cost. Means gotta keep it light, hence FG pontoons. equals 40hp outboard. lower cost etc. Can you suggest FG construction techniques , thickness, types ,etc to achieve a sufficiently strong and safe pontoon 33" wideX 26' long.. made in sections as described? or am i dreaming?? thanks again for your knowledge! )

 

Thank you KeithO for your help. Correct on all notes, however, I operate only from June to ice-up in September. Rest of time ice -free. Can you suggest construction techniques to make this work?