Aluminum boat rebuilding project - The Vonda Lynn

[cthippo]

Greetings folks, I am back messing about in boats.

A few years back one of my landlord's buddies asked if he could store his grandfather's boat at my place, to which my landlord agreed. me, being the curious type, went out and took a look at it and it wasn't in great shape, but there was potential. And so it sat for a couple of years, accumulating an ever bigger supply of leaves and pinecones.

During this time i was experimenting with underwater search and photography equipment and running into the limitations of what I could do from a kayak. Long story short, I paid $500 for a hull, a trailer, and a motor that might run. She's a 16' Starcraft with a riveted aluminum hull and a 90Hp Johnson 2 stroke outboard. Unsurprisingly the deck and transom are completely rotted out, as were the seats and, well, basically anything else that could rot.

I've gotten as far as removing the interior except for the upholstered dashboard, which is structural and will get dealt with later. Rather than replace the plywood floor I am going with open fiberglass grating so that the condition of the bilges is immediately visible. Once the deck is in place I am going to fabricate an aluminum pilothouse in place of the open cockpit because it rains a lot here.

One spot of good news is that the motor starts and runs, which is a relief. 90 hp is totally overkill, but after the first year I will try to trade it in for a 35 HP 4 stroke which should be much nicer on the fuel budget while still getting me where I want to go.

The intended use for this boat is inland wreck hunting on Puget sound and the Northwest rivers, as well as a bit of cruising. To that end she will carry my sidescan gear and underwater camera rig , and the second seat will be set up as a system operator's position. I will use an electric trolling motor with a large deep cycle battery bank for precise maneuvering over targets.

Right now i'm waiting on parts for the aluminum sub-floor to support the grating and give it something to attach to. Once I have a solid floor in, it will be much easier to disassemble the stern shroud and get the transom out for replacement. as well as replacing the dashboard and installing the house. The biggest challenges will be in building the house and installing the glazing, but, one problem at a time.

 

[bajansailor]

This sounds like an interesting project - could you post some photos of your new boat please?
And have you sketched out any ideas for your new house yet that you could post?
Re how the deck and transom are rotted out - are they aluminium as well?

 

[fallguy]

I will warn you that electric trolling motors typically have two modes, go or go. Hovering is not easy for them as the props are typically not sizable and too small to hold the boat stern to, or bow to when searching slow.

Of course, anchors do the trick.

Make sure you can size the props or you will be sad.

 

[cthippo]

Photos

 

[cthippo]

My aluminum order is supposed to show up sometime tomorrow before 9 pm, so I spent some time today scooping out as much of the residual mung in the bottom of the boat as possible and cleaning out the old rivets. I'm going to run 1/8" x 3" strips transversely to reinforce the "Z" stringers in the bilge and also give the deck pieces something to land on. I also have some 12"x24" plates coming which will eventually be seat bases. Once the aluminum subfooring is in I will layout and cut the fiberglass grating into four pieces using the old plywood floor sections as a template. In between the longitudinals I plan to install a sheet metal pan which is sealed in for the fuel tank to sit in. This will reduce it's effective height by about 4 inches and mean that any spilled fuel will be caught by the pan rather than going into the bilges.

Once the floor is in place I can remove the coaming / splash guard / whatever that thing is forward of the transom, which is cracked at all the bends from the use of an oversized motor. Once the coaming is out then the motor will get removed and the transom replaced. I have the parts to replace the plugs and rebuild the impeller on the motor, but still need to buy the carb overhaul kit and will try to replace the hoses with alcohol resistant ones as I can. I'm not sure how much strength the coaming provides or if it is supposed to just be a space to stick the fuel tank and battery out of sight. I would rather scrap it and reclaim a couple feet of usable space if that is an option.

Anyone have experience with handling towed instruments over the sides or rear of a small boat? Both the sidescan towfish and the underwater camera need to be in the water, the towfish while under way, and not get chewed up by the prop.

 

[cthippo]

Re how the deck and transom are rotted out - are they aluminium as well?

The deck was 1/2" plywood riveted to the half round ribs and the longitudinal stringers. The boat sat, full of pine needles and mung, for quite a number of years and by the time I got it the deck was collapsing under my weight. The transom is two thicknesses of 3/4 plywood which set into a cutout in the aluminum. With the shroud and motor in place I can't clearly see how it is held together, but I can peel off chunks of the plywood with my bare hands, so that's not going to work. I would like to do what I did with my 12 rowboat and replace the plywood with UHMW sheet, but this is much larger and I am concerned about the bending strength of UHMW over that span. The motor I have is already larger than what the boat is rated for, and while I don't plan to keep it forever, I also don't want to push my luck.

I will warn you that electric trolling motors typically have two modes, go or go. Hovering is not easy for them as the props are typically not sizable and too small to hold the boat stern to, or bow to when searching slow.

Of course, anchors do the trick.

Make sure you can size the props or you will be sad.

I was under the impression that electric trolling motors were throttlable down to fairly slow RPMs. Is this not correct?

I've tried anchors and multi-line moors for underwater photography, but without much real success. In the kayak days my best bet was to paddle upwind and then drift over the wrecks. Unfortunately, I couldn't see the screen on the underwater camera rig so usually it was navigation by braile from 30 feet above. One of the problems this boat is intended to solve is that it will allow one person to drive and stay oriented while the other has their head under a towel looking at the screen and giving directions.

 

[cthippo]

The aluminum for my subfloor came in today and I was pleased to find I could cut it on a bandsaw. These transverse members are mostly there to stiffen the longitudinals and give the grating something to land on. There will be a pan between the aft two pieces for the gas tank to sit in, lowering it's profile and keeping spills out of the bilge.


This is the grating I got. It's 1" thick GRP construction and weighs about 70 lbs per 3x12" sheet.

 

[ondarvr]

You can get a bow mount trolling motor with GPS, there is an anchor function that will hold the boat in place all day.

Don't use UHMW for the transom, it has no strength for this type of application.

I normally go with plywood or aluminum for the floor. FG grating works, but everything you drop goes right through to the bilge.

 

[cthippo]

OK, so running into a challenge here, the first of no doubt many.

I've riveted the transverse pieces down to the longitudinal Z sections , but when they rest on the chine ledge at the gunwales they are about 3/4" above the ribs they need to be attached to. Clearly that is not getting riveted. Do I need to make some 3/4" spacer blocks out of UHMW and through drill them for self tapping machine screws? is there a better option? I don't want to drill through the hull unless absolutely necessary (and this is not).

I think the original plywood sat on top of the ribs and below the chine ledge, meaning it was unsupported between the ribs. It's hard to tell now because the original is so badly rotted out.

 

[KeithO]

3/4 ply is very stiff so I think your assumption is correct. The flat aluminum bar on the other hand, in that orientation has no stiffness whatsoever. If you used a T section with the web vertical and just removed the web at the 2 Z longitudinal so it could be riveted, then it would indeed be stiff in the vertical direction and would provide good support even it it was not riveted to the ribs. The main reason you would want to to rivet the outboard ends is to support fore/aft loads

 

[cthippo]

Surprising amount of progress today!

I got 3 of the 4 pieces of grating cut and installed and the rest of the subfloor assembled. Saturday will be spent cutting the final piece which goes way up in the bow and sticking all the grating down to the Zs and crossmembers with stainless machine screws. I would prefer something stronger like a nut and washer, but since there is no way to reach the underside and welding on a nut isn't an option, I'll have to go with what i can. I looked for self tapping machine screws in stainless and their either don't exist or at least hardware Sales doesn't carry them (Which makes me think they don't exist). On the plus side, there is very little load on these pieces and the screws are just there to hold them down. i know they make specialized clips for this type of grating, but machine screws with fender washers will do.

Once the floor is completed I will be crawling on it to remove the aft cowling so I can get the motor off and remove the rotted transom.

3/4 ply is very stiff so I think your assumption is correct. The flat aluminum bar on the other hand, in that orientation has no stiffness whatsoever. If you used a T section with the web vertical and just removed the web at the 2 Z longitudinal so it could be riveted, then it would indeed be stiff in the vertical direction and would provide good support even it it was not riveted to the ribs. The main reason you would want to to rivet the outboard ends is to support fore/aft loads

The flat bar stock is mostly there to keep the Zs from bending and give the grating something to attach to. The grating itself is 1" thick and carries the load on it's own.

 

[cthippo]

So here is the next bug question... How do I fabricate cabin walls from aluminum shapes?

The cabin will be the full width of the boat and enclosed, with a 24" door at the rear, I need to come up about 6 feet from the deck and 4 feet from the gunwales with a stiff enough structure to survive thousands of miles of freeway driving. Riveted construction would be preferable, but I can weld it if need be. Do you have a perference for how you do this and how to mount windows in it?

 

[cthippo]

Spent the last couple of weeks mocking up the cabin in wood, which is a lot cheaper and easier than in aluminum. This gives you a general idea where i am going with the design. The structural members will be 1 1/2' square tube made of 6061-T6 alloy. The roof structure will probably be 1" tube to reduce weight and because I don't anticipate any real load on it. I'm still deciding whether I am going to learn to weld aluminum for this project (Which I know is a black art) or rivet it together. In either case, the skin will be riveted aluminum with plexi windows and foam insulated for heat and noise.

 

[bajansailor]

I am thinking 'tread cautiously' here...... how do you intend to outfit the wheelhouse that you are building?
Will it simply have a helm station and perhaps a seat or 2, or maybe a small galley, lockers etc as well?
It might be easier in some ways to carry on with a simple timber superstructure for your trial run, to see how it works (and looks when clad).
While keeping in mind the potential stability issue from adding so much (relatively) superstructure.
You mention that you will be towing this boat thousands of miles on the highways - it will be a bit like towing a very slab sided caravan, and your miles per gallon will take a hit on this.

 

[cthippo]

I am thinking 'tread cautiously' here...... how do you intend to outfit the wheelhouse that you are building?
Will it simply have a helm station and perhaps a seat or 2, or maybe a small galley, lockers etc as well?

Thanks for the feedback

The boat is optimized for wreck hunting and exploring. It will have two seats, a helm and a system operator on tractor seats with suspension. I will probably build battery boxes under the seats because it will need boat a fair amount of current for the systems, and a trolling motor for slow speed work, and also to add weight down low. No galley or much in the way of lockers, though there is some space under the dash that could serve as storage. The boat is not intended for sleeping aboard, though we might use it to travel between camping spots ashore.

It might be easier in some ways to carry on with a simple timber superstructure for your trial run, to see how it works (and looks when clad).

That's a thought. I saw someone on YouTube who used shower stall lining material for a lake boat and while it looked crappy, it was cheap and waterproof.

Hopefully I will be able to get the rotten transom off this week and replaced soon so we can put it in the lake and check for leaks and make sure the motor runs.

While keeping in mind the potential stability issue from adding so much (relatively) superstructure.
You mention that you will be towing this boat thousands of miles on the highways - it will be a bit like towing a very slab sided caravan, and your miles per gallon will take a hit on this.

Such are the trade-offs. I guess i could go with canvas, but it seems like it will always be cold and wet and inadequately protective. Open to other ideas.