Joining Plywood Butt Joints

The butt joint is the most basic method for joining two pieces of plywood end-to-end or side-to-side to make a sheet large enough to suit a large bulkhead, make a hull side panel or anything else larger than the material that is available. Within the label of "butt joint" there are various ways to do the job. Click on the diagrams to enlarge them.

A butt-strapped joint is a simple end-to-end joint, with the meeting edges glued together and with a piece of plywood on the inside to reinforce the joint.

A basic butt-strapped joint

With traditional adhesives you would have had to clench-nail through the panels and butt-straps to be sure that they would stay in place but modern adhesives are stronger than the wood, so the fasteners become redundant after the glue has cured. I would use short temporary steel screws that I would later remove and re-use for the next joint, then fill the holes with epoxy.

The strap width will vary depending on the thickness of the plywood being joined. About 15x the plywood thickness is good, so:-

135mm wide for 9mm plywood
180mm Wide for 12mm plywood
5 5/8" for 3/8" plywood
7 1/2" for 1/2" plywood

Be sure to chamfer or radius the edges of the strap before fitting it, which neatens the appearance of it on the inside of the boat and removes sharp edges that dont hold paint well. If you are fitting butt-straps between stringers in the bottom of the hull, stop the strap about 10-12mm (3/8" to 1/2") short of the stringers to leave a channel for bilge water, or you will create small traps where water can lie.

This joint is very easy to make but it does have drawbacks. It adds unnecessary weight and it spoils the neat interior surface of a boat that will have the inside of the hull exposed. It also adds a hard spot that affects the smooth curve of the hull surface, particularly if the joint is made on a flat surface before the panel is installed rather than being made in place with the panel already curved. There is a chance of the outer surface of the joint showing a hair-crack over time, so it is worthwhile to glass-tape the outside of the joint, as described below.

This joint is good for bulkheads, where a nice piece of hardwood trim can be used in place of plywood to cover and reinforce the joint on both sides. In that case the hardwood trim could be about double the thickness and half the width of the plywood butt-strap.

Taped joints are the simplest way to join plywood in small boats, with sheet thicknesses of 4-6mm. Easiest is to butt the two pieces end-to-end then laminate a length of 50mm (2") wide glass tape onto the outside. When it has cured, turn the panel over (being careful to support it properly so that the unreinforced side doesnt crack) then laminate a similar strip of glass onto the other side. Sand the edges of the tape to feather them into the plywood surface.

Taped and Flush-Taped Butt Joints

The main problem with this taped joint is that there will be a slight mound at the joint, which can be difficult to fair out so it will show, particularly with a gloss finish. The way to get around this is to recess the glass tape flush into the plywood surface. To do this, slightly bevel the both surfaces of each piece of plywood with a hand plane or a sanding machine, forming a slight slope about 1-1.5mm deep at the edge. See Step 1 in the diagram above.

When you bring the meeting edges together they will form a shallow V into which you can lay your glass tape. build up the glass tape so that it completely fills the V. When both sides have been glassed and have cured, sand the tape down flush with the plywood surface, producing a very neat and almost invisible joint.

For all of these jointing methods you will need to lay waxed paper or a sheet of smooth plastic under the joint before you start gluing or glassing, so that it doesnt bond onto the floor or work surface.

Read More..

Big Snagging List

Well its come to the time to tackle the snagging list of bigger jobs.

These are mainly the jobs I have been putting off, jobs that could wait, jobs that have occurred as a result of modification of improvements.

Today was welding back the drainage channels removed to get the toilet tank out when I thought it was leaking, after which I painted the all the drainage channels.

I need to put another coat of blacking on so I gave the lower part of the boat a good scrub, we have some good weather predicted for the next few days so I will endeavor to get the final coat on.

I have templated the seat covers for the front lockers and I have retrieved from storage the clamps for the mud box and the weed hatch and rubbed them down ready for painting and Ive fitted the the stern fender.

Other jobs done are in the engine room area include a connection for the water feed to the Cutlass bearing (white hose), final fixing hoses and wiring.

Installing the driveshaft and water seal and installing the bilge pump.

I have changed the fitting supplied by Vetus because I wanted to put a sea cock this end too, and doing it this was I can use a 14mm ID tube instead of a 10mm tube.

The bilge pump is a new design solid state unit.  Somehow it detects the water level without a float switch.  Its won design awards so I hope it will work if its ever needed.  (Update:-  I had to know, so I dipped it in a bucket of water and it worked.)

So as far as I can see I have finished in the engine room.  No doubt there will be some modifications.  I will probably change the Jubilee clips for superclamps.  Now I have discovered them I much prefer them especially in critical areas.  And I need to repaint it AGAIN!  I think I will wait until  I have a nothing else to do day.a

Read More..

D Day The Steel arrives Eventually !

30th October 2007

Finally the day came to get the steel unloaded, We hired a front loader to lift the boat from the truck.

David (9) Adam (2) and Dara (5) waiting patiently for a truck to arrive.

As usual we waited all day and had to fight to get it delivered that night so at 10:45 Pm a very annoyed driver came to town.. well he thought HE was annoyed till he met me!..

Patryk and Milo assisted the loading of the forks while I drove the machine. It took just over 2 hours to unload all 600+ pieces totalling more than 13 tons of metal. We had to floodlight the drive and light up the trailer. Only 1 piece of steel slightly bent, nothing a good hammer wont sort out.

Most of the lifts involved lifting 4 metre wide sheets of steel piled on top of each other over 4 metres high to clear the trees each side of the drive way. At least we wont have as much difficulty getting the boat out as it will be lifted out by a 130 ton crane. but thats another story.









The end result in daylight... now where to start!

Read More..

Thumbs Up For Customer Services

First heres the roof with the tape removed and the surplus grit swept off.  The weather didnt behave so it still needs painting. Oh well next time.

The photo of the mushroom vent surrounds wasnt very good on the last blog so I took some in daylight.

So on to customer services.

Ive been having a few teething troubles now the boat is being used in the real world.  First the Central Heating boiler has been problematic for a while now.  It failed last week and gave the error code for a faulty thermistor.  I was kinda pleased that something had been signalled.  A phone call to Mikuni and as usual their first class customer service had one send out FOC for replacement.  Its my guess / hope this has been the problem all along and the unit will perform as it should for years to come.

The other issue that came to the fore was the generator & inverter charger not being happy with each other.  Sometimes the charger would charge other time it wouldnt until this week it just wouldnt even try.  Also when the electric oven was on with the generator running last week and the charger on the charger would drop in and out which is not right, the generator should make up the load but the Victron controls all mains coming in so it has to be set right.

A call to Victron in Holland to discuss it with service / support started on a trail of investigation.  First I had to plug it in to shore power to see if it would charge on shore power.  Sure enough it did.

When I bought the inverter kit I decided to get the PC interface so the parameters of the Victron could be read and reset and altered without using the fiddily dip switch option.  The software and drivers were downloaded from Victron then another call to Victron and I was talked through some alterations to the default settings and hey presto everything is talking and working together. Thaks very much to customer support at Victron.

Heres a couple of screen shots of the control.  The data displays in real time.

These 2 panels show input voltage which in this case is the generator, the amps being drawn in this case by the charger, the charge voltage, chargeing amperage, the mains frequency and the mains ripple, or how clean the supply is.

Theres a whole load of other information which to be honest I have no idea about, but I think on balance the PC interface was well worth the money as I will use it to monitor things in future.  Im so impressed I have ordered the PC interface that goes into the battery monitor which can store nearly a months worth of data on what the batteries have been going through.

Read More..

Ballast

During an early dismissal from school one afternoon I raced to a scrap metal yard just outside of McAllen, TX. I had never been to a scrap metal yard before and I felt like a kid-- wanting to watch the electromagnet pick up big loads and drop them into piles. One of the guys working there gave me a hard hat and we went out to the yard to pick out metal for the ballast. I felt pretty tough in my cowboy boots and hard hat picking out scrap metal. When the guys at the yard saw the tiny Toyota hatchback I wanted to load the 800 lbs of I-beam and rebar into, they laughed. I did zoom back to the ranch riding a little lower than normal.

After another trip to the yard, I had about 1700 lbs of scrap metal at the boat shop that I thought I might be able to jam into the ballast. Even then my poor little Toyota wasnt quite finished-- I also picked up 14 50-lb bags of Quikrete at the local building supply.

A few weeks later, I picked up a cement mixer, got a few neighbors together and we started pouring the ballast. I made the mold for the pour the night before. I built it pretty stout and Im glad I did because my main concern when pouring the ballast was that the side of the mold (what would become the bottom of the keel when standing upright) would not stay square. It did stay square so I was happy.

 Boat building in hindsight: Overall, I was surprised by how well the ballast pour went. If I were to do it over again, I wouldnt use Quikrete-- Ive since learned its not as good as what you can mix yourself.

Read More..

Outboard Motor purchased

Since the boat Im building has a retro look, I wanted to get a classic outboard for it. After doing a lot of research on older outboard motors and joining the national Antique Outboard Motor Club (AOMCI), I attended a swap meet of our local Great Lakes Chapter of the AOMCI. I was focused on mid-fifties Mercurys and Johnsons in the 15-20 hp range and my preference was for a Mercury Mark 25 (18-20 hp depending on year). I had previously looked at a 1954 Mark 20, but the owner had a different idea about its worth than I did so I walked away on that one. I had another lead on a 1956 Mark 25 that was for sale by the brother of the guy that fixed our computer. He had a picture of the motor sent to my Blackberry and it appeared to be what I had in mind. At the swap meet, I did not find anyone selling a Mark 25, but did learn they were generally good motors and the 1956 Mark 25 had several improvements over the earlier Mark 20 and Mark 25 models. I was also advised to find a motor that already had the set-up for remote steering, shift and throttle control as these items would be hard to find separately. Having gained some good advice and a good contact for working out any issues I might have once I found something to work on, I pressed on.


The next day, my wife and I went and looked at the Mark 25. It had the remote control set-up, but needed a bit of TLC. Unfortunately his father was supposed to meet us there with the fuel tank for it but he could not find it and may have been lost in a recent move. I was told this motor had a new waterpump put on it two years ago and had been running fairly recently. The compression seemed good by pulling the starter rope. The motor colors are Sarasota Blue/Sand Tan. My wife thought the color combo was retro and would look cool. So knowing an old motor is a bit of a gamble, we reached an agreement on price, loaded it up and took it home.


It seems to me at this time that Sarasota Blue/Sand/Tan may be a relatively rare color combination. Ive seen pictures of Mercury Green/Sand Tan, Sunset Orange/Sand Tan and Marlin Blue/Gulf Blue on other Mark 25s in pictures on the web of various antique motor club meets or in the Antique Outboarder magazine. I havent seen this color combo yet. It reminds me of a 1956 two tone Chevy Belaire. Guess Ill find out as I learn more. I ordered and
received a service manual and fuel connector from East Coast Marine and hope to purchase a fuel tank, hose etc. soon and get this baby in a garbage can full of water and see if it fires up. Heres hoping I have an outboard and not just a pretty boat anchor.

March 6, 2010 Update:
I put together a 3 gallon plastic fuel tank with quick disconnect to tank fittings, hose, primer bulb and the connector to the motor. I did a 50:1 ratio mix by putting 2 1/2 oz. of two cycle oil and a gallon of gasoline in the tank....shaken, not stirred. Since it was a 50 degree sunny day, this was my chance to see if it would start. Using the bottom from a defunct shop vac, I put it under the outboard and filled it with water which was about 3-4" over the top of the cavitation plate. I hooked up the fuel line, opened the tank vent, squeezed the primer bulb about 10 times until fuel could be felt in the bulb and I could smell it. Then I set the choke and gave the starter rope a pull...nothing except water sloshing all over. I enlisted my daughter to hold the back of the motor to stabilize it while I gave another pull...nothing. Another pull...nothing. Took off the choke, squeezed the primer bulb again and gave another pull and hot damn...it started running! (Big smile on face). I saw a stream of water coming out the hole at the top of the lower unit indicating the water pump was doing what it should, and then I slowed the motor down to shift speed and shifted into forward. Water started leaving the barrel as the prop churned it up. Tried reverse and saw that it worked and then back to neutral. I revved it up a bit, then slowed it down and ran it for a while so some pictures could be taken. I disconnected the fuel line and it ran for a couple of minutes until the fuel in the carb ran out. Hurray....it all works!

Read More..

Back In The Saddle Knee Update

I spoke to my other neighbor today.  She said she heard the explosion as well, in fact she said she felt it as well.

Its been a little de-motivating to be honest, but on the upside its pretty much agreed that I was very lucky not to have been injured.  I agree.

I decided to console myself with setting out the instrument and control panel and the steering pump.  This is the rough draft.

I have also drawn up and sent of for pressing the lids that will cover the lockers on the stern.  Hopefully I will get them next week.  I have a canopy maker coming over on Monday to start templating for the stern pram hood.

Finally the knee.  Ive had a long term injury to my knee from a torn cruciate ligament.  For 20 + years it has been a dull ache, which from time to time flares up especially after skiing.

Well apart form having a sizable dent in my knee cap and a very large bruise my knee actually feels better.  So hopefully when the bruising and swelling goes down it might be mended.  Fingers crossed.

Read More..