The Decks

In the last post I had rough cut the white beech deck strips to length. Over the last 10 days I have completed the decking, at least for the time being! A series of photos shows the steps in the process.

The strips were trimmed to fit lengthwise and positioned using 4 mm thick plywood spacers. When all looked OK the strips were taken up, coated with epoxy and laid down in a bed of thickened epoxy. This white beech has an oily or waxy feel to it and so I wiped the surface with an acetone soaked rag before putting the epoxy on. The spacers had to be wrapped in thin plastic; cutting up the plastic garbage bag was a nightmare - static electricity stuck the pieces of plastic to my hands, the scissors, the benchtop, etc. Bear in mind that I needed a couple of hundred of them!

The section at the far side of this photo has the "paver" clamps applied. Unfortunately, once the pavers are there it is impossible to clean up any squeezed out epoxy. There must be a better way. The section in the foreground is waiting for the pavers.

Here is the foredeck after sanding and cleaning out the epoxy from the gaps, a dreadful job but fortunately there wasn't a lot of places where the squeeze came near the top of the groove.

I gave all the margin planks a coat of epoxy before applying tape to all the strips and the margin planks. Then the messy business of putting Sikaflex 291 into the grooves. I worked out the volume of the grooves roughly and bought three tubes of Sikaflex. The black stuff gets everywhere and there is quite a lot of wastage - I had to buy another 2 tubes. Four and a bit tubes did the job.

Here is the after deck after pulling up the tape which came up quite easily and cleanly; I was pleasantly surprised! I went over the whole area carefully with the belt sander (80 grit) and then with the random orbital sander (120 grit).

The white beech strips were coated with Deks Olje number 1 flooded on with a brush until no more was taken up. The white beech didn't want to take up much of this oil and I will put more on later. I prefer the satin look and none slip nature of  this oiled surface; I've done it before and it seems to wear well. The margin planks were given another coat of epoxy and the last 2 photos taken.

I think it looks pretty good!

There won't be anything posted here for some weeks because I am going away for a holiday in the UK. More when I return.

Propeller and Deck Planking

In an attempt to clear up my confusion about the propeller calculations I bought a copy of Dave Gerr's "Propeller Handbook".   This book has far more information than I need but I will follow his process carefully to determine the diam,eter and pitch of the propeller. It will be interesting to see how the result compares with the prop that is on the boat.

I have been working on the planking of the deck. There will be a "margin" plank 65mm wide around the gunwales and the coaming. Along the sides of the boat the 2 planks (along gunwale and around cockpit coaming) will over lap so they will be done in a single piece. I made templates out of cheap plywood for all the pieces because they are all curved. The templates were laid out on the planking stock to minimise waste. The stock was marked and the pieces cut out. Each piece was carefully trimmed to fit in its place and then they were all glued down. A couple of photos show the pieces being glued using 200 mm square concrete pavers.

One drawback of using pavers is that they make it diffcult to clean off any squeezed out epoxy so this has to be removed after it has set and the pavers removed. The trimming of the pieces and gluing them down was done in stages over a period of 3 days.

Here is a photo of the aft deck with the margin and king planks in place.

The space in side is going to be planked with parallel strips of white beech. The beech I bought was rough sawn 100 x 50 mm and 3 metres mm long. I put it through the thicknesser to reduce it to 45 mm thick and then through the bandsaw to get strips 45 x 8 mm.

I rough cut and laid the strips on the deck with 4mm gaps. Here are photos of both fore and aft decks with the strips on.

It will take 2 or 3 days to cut the strips accurately and glue them in pace - more paver clamping!

Maiden Voyage and Test Run Numbers.

There have now been a number of launches in my local lake ad I am delighted with the outcome. There is still a lot of work to do on the woodwork and the final battery arrangements and controls. This short video (thanks Paul) shows the maiden voyage.

I am disappointed by the whining noise from the motor; it is a 3 kW BLDC motor from Golden Motor in China. I will build a sound insulated cover for it and hope this will quiet it down. Apart from that it works well.

By weighing the vehicle and trailer with and without the boat I find that the boat with the temporary batteries weighs about 430 Kg. With me (about 70 Kg) at the front of the cockpit the boat floats level about 30 mm above the DWL. I worked out that the area on the DWL is about 4.4 sq metres so the volume of the 30mm thick slab is about 130 litres or 130 Kg. The total weight (displacement) of the boat when at the DWL is 430 + 70 + 130 = 630 Kg. This is close to the figure of 620 Kg given by the designer.

With the boat floating 30 mm high I made some test runs and took measurements of speed, amps, volts and prop RPM. See below. From the measured numbers on the left I calculated the power required in watts and equivalent HP.

NOTE. This table is a revised version of the original; The measured current was low by a factor of 3.33 and the the calculated speed and slip have been removed. 

The power required is lower than I expected and I believe this is, to some extent, because the boat is floating high so less water to displace and less wetted area. I caught some weed on the prop and had to paddle the boat to the bank so I could clear it. Sitting on the gunwale with a single ended paddle I managed about 1 knot so the boat is easily driven.

Water line length is about 15.25 feet so hull speed is around 5.25 knots. In the video the boat is travelling (right to left) at between 4 and 5 knots.

The prop is second hand from EBay. It is 11.5” diameter x 15” pitch. The calculated slip is much higher than the 40% number I had in my mind and this puzzles me. The calculated slip decreases as prop RPM increases. I don’t understand this at all!

It was (still is) my intention to replace the EBay prop with a better one after making some test runs. I was thinking 12” or 13” diameter and more pitch. On the other hand the EBay one works so need to know what would be gained by changing it and to what.

Getting Close to a Test Run

There has been a bit of "two steps forward and one step back" progress over the last few weeks. That said I'm hoping to put the boat in the water sometime in the next week or two.

The boat is on the trailer. This is a fiddly business with the boat being lifted on and off the trailer while the axle is moved to balance the whole thing with the right amount of load on the tow ball. The keel rollers and bolsters have to be adjusted so the boat will clear the mudguards. Once this was done the supporting V-block on the winch post fouled the pulling eye and winch hook so the winch post had to go back to the maker for modification (a two hour drive each way). Here's what the boat looks like on the trailer.

The modified winch post.

And the aft end of the boat.

Fitting the rudder seemed to have more backward than forward steps! I fitted the bracket to the skeg while the boat was still upside down. It is held in place by 5 8mm metal tread screws. I drilled the holes in the skeg oversize and filled them with thickened epoxy before the paint went on. With the bracket clamped in place I drilled and tapped holes into the epoxy for the screws. Then coated the mating surfaces with Sikaflex marine sealant, dipped the screws in epoxy and screwed them in.

With the boat up on the trailer I went to put the rudder in place and found there was too much rudder blade to allow it to lift enough for the thread end of the rudder shaft to get into the hole in the bracket. Two ways to solve this problem: take the bracket off and refit with the rudder in place or cut some off the top of the rudder blade. The bracket was supposed to be permanent and I knew it would be difficult to remove the screws so I cut a strip off the top of the rudder and cleaned up the shaft where the weld had been. The ruuder blade is 6mm stainless steel and so the paint was damaged. In the photo above it is waiting for some more topcoat.

When I put the rudder in place the threaded part of the shaft wouldn't pass through the hole in the bracket - 16mm hole in bracket 20mm thread on rudder shaft. . Drilling out the hole in the bracket on the boat was impossible; it is 10mm thick stainless steel and hand held drills are not up to this sort of job. The bracket had to come off and getting the screws out was more difficult than I expected. The technique is to heat the screws to soften the epoxy. A soldering iron works for small screws but even my big tinsmiths soldering iron held in place for 10 minutes wouldn't do it. I had to get under the boat with my high temperature gas torch and apply a frightening amount of heat. Eventually the screws were out but the Sikaflex still held on quite well. Surprisingly the paint work wasn't damaged at all. Drilling the bracket on the drill press took only a few minutes and refitting it was messy but quick - lying under it with Sikaflex and epoxy falling on me was not nice!

Inside the boat the motor, prop shaft seal, bearings, etc are all in place. I tested the electrical side of things on the workbench so the batteries and control box only had to be lifted into the boat and hooked up.

The batteries are second hand car starting batteries totaling 48 volts and will only be used for a few short test runs while I measure the current and propeller shaft RPM at various boat speeds. Once the current is known I will make an informed decision about the battery capacity (amp hours) needed for a day's cruising. Once the prop RPM and boat speed are known I will decide what to do about the prop. The one on the boat at the moment is 11.5"diameter (I would like 13") and 15" pitch (I think I need 17" or 18").

The box above has volt and amp meters, a keyed on/off switch, a forward/reverse switch and a speed control knob. Again this is only for testing the boat, the final controls will be more permanent and hopefully simpler. The green cargo straps will hold a cover down over the batteries to stop them moving about.

Painted, Turned Around, Some Engineering.

The hull is painted now. I finished sanding the original undercoat and then gave it another coat of white undercoat mixed with dark green topcoat about 50/50. Another very light sanding to get rid of the few flies and then 2 coats of International Paint's Donegal Green. I left the boat alone for a few days to let the paint harden and then fitted the rudder bracket under the skeg and a 10mm thick strip of HDPE (plastic) along the bottom of the keel. I merged the HDPE into a half round brass strip that curves around the forefoot and up the stem. With that done the boat was lowered back down to floor level. Here she is:

The boat is resting on a trolley so that it can be rolled out, turned around and rolled back in. The legs in the photo above are to stop it falling over sideways while the slings are removed and then replaced after the move.

I had 4 helpers to do the pushing, pulling and balancing so the move went fairly easily except that one of the wheels lost is solid rubber tyre as the boat was spun around. These cheap and cheerful hardware store wheels look substantial but are not very strong.

here's the boat back in the shed and on its supports so that I can work on the inside.

Inside the boat I started assembling the prop shaft, pulleys and electric motor. The shaft bearings are in place and it is all fitting together nicely.

That's a temporary floor and the rubber mats are padding for my knees!

Hatch Cover

Ten days ago I was away enjoying a few days sailing. On the last day I tried out the rope ladder that is supposed to make getting back on board possible; it is only a small sailing boat but has quite high freeboard. As expected the rope ladder idea isn't very good. When you put your foot on the bottom rung your foot goes under the boat and it requires a lot of upper body effort to counteract this. It was possible but I strainf all sorts of muscles in my body and arms! I will invent a better ladder!

When I got home and back to boat building the next job was to finish painting the outside of the hull. To make this easier I lifted the boat up onto two sawhorses. This was easy enough to do using a couple of chain blocks - no arm strength needed. Here it is:

The white undercoat needed a light sanding and you can see all the paraphernalia under the stern. I managed to do less than an hour before the clicking and grating in my shoulders and muscle pain made me stop. It is now a week later and I have just managed to do another half an hour on the sander. In the meantime I have been "resting" which is something that I am not good at.

To fill in the time (light duties) I finished the cover or lid for the access hatch in the stern deck. The hatch is there to allow access to the steering arrangements. The cover is 420mm outside diameter and I wanted to display the boat's name in it. Almost the hardest part of the job was deciding on a name! Not very original but I settled on "Lady Susan". This is a "gentleman's launch" and the gentleman often named the boat in honour of his wife so we have Lady xxxx. Susan was my late wife.

The outer ring is one piece of cedar. There is a 12mm thich plywood disc epoxied inside it and the inlaid pieces started out about 3mm thick before they were sanded flat. There about 60 pieces of inlay all cut out on my small CNC mill with a 1mm diameter end milling cutter. The timber came from the scrap box.

I also made a couple of name plates for the sides of the hull at the bow.

There are 3 of them because I made one as a test piece. It has a couple of imperfections so I made 2 more, neither of which were as good as the first one!

Bits and Pieces!

Not a very imaginative title for this post but it is what I have been working on for the last 3 weeks. The weather has been very hot here in Brisbane culminating in a 44C day last Sunday. In my tin boat shed it is usually 2 or 3 degrees hotter and so I have been lucky to put in 4 hours each day. Hence slow progress on bits and pieces.

I made the two pulleys for the PolyV belt drive between motor and prop shaft; the 4:1 ration will give me 1000RPM at the propellor.

I made a bracket to mount the motor. Plywood covered with fibreglass, glued together, the corners filleted and then tape applied to reinforce the whole structure. This is the third bracket in a trial and error approach to design!

The motor is mounted on an aluminium plate with slotted holes for adjustment of belt tension.

 Here's the view from the other side showing the motor. It's a 48V 3000 watt (4HP) motor from Golden Motor in China.

The section of the gunwale around the stern had to be laminated from 5 x 6mm thick strips. I soaked these for 4 days and then bent them around a former. After they had dried out, another 3 days, they were glued and clamped around the former again.

Here is the cleaned up and fine tuned section of the gunwale glued in place. The rest of the gunwale was done in 2 sections starting at the bow. Both these sections were laminated in place from 2 x 12mm strips. The mid ships section was fitted last with scarf joints. I definitely need more clamps!

The cover strip on the top of the coaming was also laminated in place using 6mm thick strips again soaked, bent, clamped and allowed to dry out before being glued in place. Here is on of the strips being glued; this is about the first job where these spring clamps that I got for a bargain price have been useful.

While all the above was going on I had cleaned up the paintwork in the forepeak and given it 2 coats of topcoat, this was much easier to do while I could still reach through from above. With that painting done I glued down the 2 ply panels making up the deck. There will be covered by the deck planking.

Propellor, Etc.

The propellor is a tricky thing to get. The simple solution is to buy a new one - around $600. The problem with this is that you have to specify the diameter and pitch. Diameter is fairly straight forward, as big as possible but allowing sufficient clearance between it and the hull to avoid cavitation problems. This gives me 13 inches diameter as a maximum. The pitch is more difficult because it depends on hull speed, the propellor RPM and a factor called "slip".

Hull speed for a displacement boat can be calculated as factor multiplied by the square root of the waterline length in feet. The factor is somewhere betwwen 1.0 for a barge and 1.4 for a slippery hull shape. Working on a factor of 1.3 and LWL of 15.25 gives a hull speed of 5.1 knots.

The formula that relates boat speed a, propellor pitch and RPM is:

        speed = RPM x pitch x slip / 1215 (1 knot = 1215 inches per minute)

Rearranging this to calculate the pitch:

       pitch = (speed x 1215) / (RPM x slip)

Putting numbers in gives:

      pitch = (5.1 x 1215) / (1000 x 0.4) = 15.5 inches.

I started looking for a secondhand  13 x 15.5 prop and found one on ebay and bought it for $120. This prop is 11.5 x 15, smaller in diameter but close in pitch. I will use this prop to make some test runs and then buy a larger new one with the correct pitch and then sell the first one on ebay.

Here is the propellor and shaft sitting temporarily in the boat.

At the other end of the prop shaft are some bearings and the electric motor. The bearings are visible fore and aft of the two floors. The plywood bracket holding the motor isn't quite the right shape and I will make a new one. The motor will drive the prop shaft with a poly vee belt around two pulleys giving a 4:1 reduction - motor speed 4000 RPM, prop shaft 1000 RPM.

The pulleys are easy enough to make (aluminium and I have a big enough metal turning lathe) and I have found a place that will cut the keyways in them for a reasonable price. I could cut the keyways on my lathe but it is tricky to set up and slow to do.

Another accomplishment over the past 2 weeks has been replacing the motor on my table saw. I started ripping timber to make the gunwales and capping strips for the cockpit coaming and the table saw would only run for a few seconds before it tripped the circuit breaker. I thought it would be easy! 2HP motor is a common size and would be available off the shelf. Took the old motor to a shop and found that it might be easy to fix (good) and that they didn't have a replacement motor in stock (bad). It turned out that the old motor was dead and the new one took a week to arrive! Of course the holes in the new motor's feet were in different places to those in the old motor, sigh!

Much nicer than the old motor. Maybe I should buy a new V belt - the old one is looking a bit tatty!

Steering Wheel

I've been making the steering wheel. This has fitted in well around the Christmas interruptions and my lathe, drill press and CNC mill are in a cooler workshop - it is very hot here at the moment!

I want a wheel with a ring and spokes with handles - see the mockup in the previous post. I had already made the hub and its aluminium bush. This is visible in the left hand photo below. There is a slot through one end of the bush with a pin through the axle to stop it turning. Also in this photo are the pieces of the ring temporarily assembled with their loose tenons. The six segments of the ring were cut out on my small CNC mill; they are oversize to provide for the eventual clean up. They had to be flat on the outside with square corner so they could be stood on edge in a jig while the slots for the loose tenons were milled. The right hand photo shows the sticky mess after gluing all the pieces together.

With the glue set I roughly cut the outside to shape and trimmed off the excess of the tenons. On the lathe the ring was held on the outside of the chuck jaws while the outside was carefully finished to size and one flat side faced off. Then a "jam chuck" was turned in a piece of scrap timber; this has a recess turned in the face which is a tight fit on the outside of the ring. With the ring hammered into the recess the inside and the other flat face can be turned to size. The LH photo below shows ring and hub  on the assembly board.

The RH photo below shows the setup for drilling the holes in the hub and ring. These holes have to be accurately drilled or the spokes simply will not fit. The phot shows the hub being drill. It is clamped to the jam chuck used on the lathe which now has a ring of holes in it exactly 60 degrees apart. The jam chuck can rotate on a bolt which holds it to a vertical board on the drill press table. The board also has the same 6 x 60 degree spaced holes. At the 6 o'clock position a drill is locking the rotating chuck to the fixed support while one hole is drilled. Then the chuck is turned by 60 degrees and the next hole drilled. The ring was drilled with it jammed into the chuck.

 The LH photo below shows the wheel assembled with pieces of dowel and no glue. It went togehter very easily - it is far easier to get those holes right than to position and size the photos on this page! I turned 6 handles with a hole the same size as the dowel and then glued the whole wheel together.

Now I am debating whether to stain it or leave it natural.