Here is a list of all the postings Gareth Jones has made in our forums. Click on a thread name to jump to the thread.
|Thread: Shemarah II|
The last couple of days has been spent fitting the water pump to dump water overboard from three outlets on the port side and one on the starboard. There is a single inlet to the pump mounted about 2 inches below the waterline.
The pump is an MFA 650 gear pump which is self priming. It is mounted in the bottom of the hull, just behind the main motor and between two of the frames. Running on 12 volts it takes 0.65 amps but a lower voltage will probably be used to produce a more realistic flow and reduce the noise. The initial trial will be carried out using a slave speed controller but on Dave Milburn's advice, an adjustable voltage regulator, available from MFA, will probably be used in the end.
All of the pipes through the hull are the same, made from 3/16 brass tube with a short length of slightly larger tube glued on the end to give the flexible silicone tubing a more secure grip. A piece of 6 mm ply was used to reinforce the area where the tube penetrates the hull. Each one was glued in place with araldite and a long setscrew and piece of larger diameter brass tube was used to clamp the assembly in place while the glue dried.
|Thread: Time Off!|
Lovely set of pictures Colin, I especially liked the ones of the propeller blades but it was difficult to judge the scale. I would have imagined they would be much bigger than they appear. However the photos that caused me great concern are the ones showing the deck planking.
Earlier this year my wife and I attended a model boat show in Menston near Leeds. We were only attending as visitors, not exhibitors, but my wife took her restored model Sharpie, Secret Princess, as she wished to show it to a friend who we knew would be at the show. The model is a 30 inch free sailing yacht originally built in the 1950's and a view of the deck is shown in the photo below..
It attracted quite a lot of attention and most people were very impressed by the standard of restoration work Elizabeth had carried out. However one particular individual was very critical of the deck planking, because there were only two continuous planks between adjacent joints. He was adament this was wrong, it did not comply with Lloyds insurance regulations and no boats were ever built like that. Despite my wife's protestation that it was a 'toy' yacht and not intended to be a scale model, the critic insisted that to do it properly, she should remark the deck with three continuous planks between each set of joints.
The pictures of the Queen Mary clearly show that there is only one continuous plank between each set of joints. This leads me to the inescapable conclusion that the deck of the Queen Mary has been built wrongly and the ship must be unsafe if it does not comply with Lloyds rules. The ship should be withdrawn from service immediately. I feel I must tell someone, Cunard and Lloyds at least. I have already lost a nights sleep over this, who should I inform Colin?
Sorry Colin, just realised this is in the wrong place, should be under Full sized ships - Queen Mary
Edited By Gareth Jones on 11/10/2011 17:09:42
Edited By Gareth Jones on 11/10/2011 17:32:11
|Thread: Electric motor temperature sensor|
Thanks for that. I think I will try one of those, it has the advantage of being adjustable which might be useful in the final installation.
|Thread: Shemarah II|
In principle there will be two 'trays' of electronics in Shemarah. The forward one will hold the power supply fuses and the main switches which will be accessible through the hatch forward of the wheelhouse. The aft tray is shown below and will hold the P100 noisy thing, amplifier a radio controlled switch unit and any other odds and sods that turn out to be required. The tray itself is just a piece of 3 mm ply with the boxes temporarily stuck on with double sided tape below.
I have made a card deck template with the main access holes cut out as shown below.
Heres the aft electronics tray being inserted through the access hole where the main superstructure will fit.
And heres the tray with the end inserted into the start of the two pieces of 6 x 6 mm brass channel which act as rails to allow it to be slid in to the rear of the hull.
The rails are supported on short pieces of strip timber glued to the flanges of the hull frames. The picture below shows the tray slid into position at the back of the hull centre section.
The idea is to have a single loom running along one side of the hull to connect the two trays together. The receiver will be mounted high up on the side of the hull well away from all the power wiring. The speed controller will be on the other side. A flying lead with a multi pin socket will run from the aft tray to a point at the rear of the superstructure access hole. A mating plug with a flying lead will be fitted on the superstructure to connect up the lights, audio speaker and radar antenna drive. Pretty well all the wiring can be made up and tested on the bench before fitting the two trays into the hull. This should result in a reliable neat installation with the minimum of scarred knuckles through trying to work through a little access hole with minimal visibility of what's going on. The whole lot can be removed for trouble shooting or modification without tearing half the boat apart.
Well that's the plan anyway. Every model boat I have made so far has ended up with a major modification at a late stage in build when its really awkward to do. Hopefully this time will be different.
Edited By Gareth Jones on 09/10/2011 16:15:11
|Thread: Electric motor temperature sensor|
Thank you for those few kind words Telstar.
As another option for Barzo, in my current build project, Shemarah II, I am planning to fit a small water pump, not to cool the motor, but to simulate the water flow you see from several points in the side of the hull. I guess the largest of these flows may be engine cooling water.
The pump I am planning to use has been robbed from my model aircraft flight box where it was used to transfer fuel to between a 5 litre bottle and the aircraft tanks. Judging by the number on the pump it is part number MFA 650 and although its many years old, it is still available from Sussex Model Centre for £10.99 (other sources probably exist) where it is advertised as a fuel/water pump.
I have tested it in the sink and at 12 volts it produces a very healthy flowrate and takes approximately 0.65 amps. It is a gear pump and self priming at least up to 6 inches above the water level (couldn't get any higher as that's the limit of my tube length). Its a bit noisy and the flow at 12 volts is greater than I need so I am planning to run it from the main 12 volt battery but via a 4.8 volt BEC power supply unit. At this voltage is quieter and still seems to give enough flow for my needs.
Unfortunately I have never designed a motor core or a winding in my life - I am beginning to wonder what I have missed. I have tested a number of motor/ propeller combinations and looked at motor performance curves and I think the simplest and most useful tool to use is a lazer tacho, available for around £10 on the web. Don't worry too much about amps and volts.
Measure your motor's free running speed at full throttle with the propeller removed and the boat out of the water. I have found the best place to put the reflective sticker for the tacho is on the flexible coupling between the motor and prop shaft.
Next measure your motor speed in the fully loaded condition with the propeller fitted and the boat static in the water. If this loaded speed is between 65 and 75% of the unloaded speed your combination is pretty well spot on.
If the loaded speed is less than 50% of the free running speed your propeller is bigger than optimum and if you spend a lot of time at high power, your motor will get hot. Solution - fit a smaller diameter propeller.
If your loaded speed is greater than 90% of the free running speed your propeller is too small and you wont get much thrust. Solution - fit a bigger diameter propeller.
There are lots of other subtle factors you can consider like the type of boat, how you want to sail it and how much friction there is in the drive train, but in my experience its best to keep this analysis simple.
|Thread: Shemarah II|
|The reinforcing bars have now been added on to the transom. Following Bluebird's advice I used a strip of 1/32 ply to act as a template and get the strips evenly spaced across the area. |
The strips are 2.5 mm Raboesch styrene attached with thick superglue, which gives just enough time to slide them to the right position and fills the gap around the edge of the strip pretty well. Heres the final result.
Before I can do the strips on the side I need to build up the bulwarks on the aft end where they are stepped inwards to provide a stowage area for the trawl doors. Before I can do that I need to fit the deck. However before I commit myself to removing access to a large area of the 'innards' I am going to fit a sliding tray on which some of the electronics will be mounted (Noisy thing sound system, sound switching unit, amplifier and a switching unit for the lights and anything else I decide to control from the radio system. The main power distribution, fuses and switches will be on a similar sliding board in the front end with working access through the main hatch forward of the wheelhouse. All will come clear in the next set of photos I hope. (no smoke and mirrors here)
|Thread: Electric motor temperature sensor|
I also struggled with 60watt's explanation but after a bit of thought I think I understand the point he is trying to make.
You are probably correct that at 20 volts, the propeller you are using is too large a diameter for the motor and it is running well below the motors optimum speed and therefore quite inefficiently, generating lots of waste heat.
The following figures are not necessarily correct but I am just trying to illustrate a point. Assume your present set up takes 20 amps at 20 volts and has an efficiency of 40% the output power will be 160 watts and waste heating will be 240 watts.
If you run it a lower voltage with a bigger propeller your combination might be 40 amps at 10 volts. However if this combination is closer to the optimum speed of the motor the efficiency will be higher. Lets say its now 50 %, the output power will be 40 x 10 x 0.5 = 200 watts and waste heating 200 watts. However the bigger propeller will in itself be more efficent than the smaller one so the benefits will be even greater.
I think 60watts suggestion is not just try a bigger propeller, but try a bigger propeller at a lower voltage. I hope this makes sense to you (and 60watt)
|Thread: Shemarah II|
I dont think my build quality is that exceptional, lots of people have much better practical skills than I do. I like to think that I pay attention to detail and I am quite thorough in all my control, wiring and propulsion systems installations, but then that was my job for 40 years.
Unfortunately we are not often able to visit the pond at Goole for the main sailing session on Saturday sfternoon. We live about half an hours drive away but on Saturday our daughter works at a riding stables half an hour away in the opposite direction and since we have to pick her up mid afternoon its a bit awkward.
Yes I am enjoying the build, its just taking longer than I expected. I seemed to able to find more time for boat building when I was at work. Now that I have retired there seem to be so many other things to do and I dont appear to be able to get up at 5:00 am for a couple of hours in the shed any more.
Today has been spent fitting the half round rod on the anchor recess which is now complete apart from the tube up to the deck which will have to wait until the deck is marked out and fitted.
This afternoon I have made and fitted the two transom doors and rollers. Here are the individual parts of one side.
The water pump idea has been put on standby over the last few days and I have been fixing the steps in the hull and installing the anchor recess. I originally built the steps in at an early stage of the hull construction as I was reluctant to have to cut a slot in the side of the hull at a later date. They were covered with a temporary ply plate when the hull was fibreglassed. However due to an error reading the drawing (it is confusing) I thought the scuppers intersected and cut through the steps on each side. Therefore I cut the top section off, not very neatly, because I assumed I would have a 3 mm slot to tidy the gap up. Unfortunately I later realised, after looking at some photos, that the step structure is continuous and it is the scuppers that are interrupted. Rather than try and reattach the bits I cut off I decided to bite the bullet, cut out the existing steps and make a new set. The picture below shows on of the completed assemblies.
The next step was to cut the recess where the anchor fits. This was a bit tricky to size and locate as the view on the drawing shows the recess at an angle. However reference to my collection of photos helped and I marked and chain drilled the hull in what I think is the right spot. The piece of string marks the waterline which was one of my main references.
There is some supporting structure behind the cut out which had to be cut away but helps support the sides of the recess.
Lining up the hawse pipe that the anchor chain will run down was rather confusing. The drawing plan view does not line up with where the anchor sits. It does not seem logical that the connecting hawse pipe is curved or kinked so it was back to the photos again for help. These solved the problem as they showed the location of the winch on the deck plan is not quite correct, it is angled differently from the real position. The back, top and sides of the recess have been glued in position and will be ready for sanding flush with the hull skin tomorrow.
My half round reinforcing has arrived and I will be practising fitting the first few short pieces around the sides and top edges of the recess. I am planning to have a working anchor but at the moment I am not sure how I will do this. I have looked at the Krick working winches but they are expensive and I am not convinced the anchor will fall under its own weight because of the friction of the drums, winch gypsy and the hawse pipe. They also need to be operated from a proportional channel of the radio system which would be a nuisance. At the moment my thoughts are to uses a drum type sailwinch to raise and lower the anchor. It may not fall quite as fast and freely as real life, and it may be lifted up a bit too quickly. However on cost and simplicity of engineering it looks a promising option. I think I could operate it from the gear up/down switch on my transmitter which would be a neat solution if it works. ( Mr Milburn - Can you slow a servo down in only one direction using a Servomorph?)
While cutting the hole for the hawse pipe it dawned on me that I have another problem to overcome in the same area. There are a number of lights on the mast and the wiring needs to run down the inside - easy enough I think. However the mast sits close to the bow on a compartment that is now completely enclosed. In order to get wiring to it I will have to cut a hole into that compartment and through several other frames. I guess I will put in a piece of tubing as a conduit to run the wiring through. While it will be a bit tricky now, it would have been a nightmare job if I had not realised till after the deck was fitted.
Shemarah had a couple more outings to the Goole and York ponds at the weekend and the removable ballast principle was proved to work OK so it looks like a go-er.
The last couple of days have been spent making the supporting structure for the Kort nozzle. This is not shown on the plans but can be seen on photos of the ship out of the water. The actual design does not look very elegant, and would seem to me to be a bit draggy but then I know nothing about hydrodynamics. The upper supporting structure was made from 1.0 mm plastic sheet. It was really awkward to make as it is all different angles and curves and it is almost impossible to take proper measurements on the model. It was all built by trial and error and I have thrown away two or three examples of each part before I got them all to fit. The lower supporting 'fill in' piece was easier and was just made by cutting and shaping a piece of 6 mm ply.
Having assembled all this I found the rudder was no longer aligned and was stiff to rotate as the stiffness of the complete nozzle mount had removed any compliance. The rudder bearing tube was removed by inserting a soldering iron into the bottom end and allowing the whole thing to warm up and soften the araldite. The tube was removed and the tube and hole were then cleaned up and reglued while the whole assembly of nozzle and rudder were held in alignment. Its now fine and the rudder is free to move. I always use araldite in this sort of situation as heating the metal part with a soldering iron or small blowtorch will soften ithe glue. It works well if you need to remove a propshaft tube for example, although it might be risky in a plastic hull.
The next job, while I am waiting for my half round reinforcing strips to arrive, is to fit a small water pump to eject water from three holes in the port side of the hull. I guess one of these is a cooling water flow, one may be a bilge pump but what the other one is I have no idea. However they are quite prominent on photos of the real ship so I have decided to include them as a working feature.
|Thread: Marblehead yacht|
Could you give us any more details of the Marblehead you have for sale.
What is the hull made from, wood or fibreglass?
Do you know the design name?
Does it include mast and rigging?
What type of sail winch would be needed for it - drum or lever type?
Could you post any photographs of it?
|Thread: Shemarah II|
Today I have modified the ballast arrangements and Shemarah has been back in the bath to test the balance. I have added an additional pair of ballast weight platforms just forward of the centre of the hull.
The photo above shows the left hand pair, each with a screw/stud to locate in a hole in the bottom of the ballast weight and a recess to accommodate the screw which holds the lead sheets together in each pack.
Each pack is held together by a screw which passes through all the sheets and engages a rather elegant stainless steel knob to allow the whole pack to be easily removed. I will probably replace the threaded locating studs with plain brass rods with a slight taper in due course as the threads tend to create slivers of lead each time the ballast weight is replaced. The front pair of ballast weights weigh 2.35 kg each and the rear pair weigh 3.35 kg each. Assuming the total all up weight of the model ends up around 25 kg (60 lb), I will have 11.4 kg (approx 25 lb) of easily removable ballast, leaving the hull weighing around 13.6 kg (35 lb) when it is lifted in and out of the water.
I have also moved the ballast weight at the back of the hull forward by two frames to allow it to be fitted lower down. Tests on the pond and in the bath suggest the model will not be particularly lively in pitch so moving the ballast forwards will not adversely affect the overall stability. Each individual ballast weight can be adjusted by adding or removing sheets to get the final required weight. Its close enough now to allow the model to be sailed for test purposes, or just for fun.
The next step is to begin marking the hull ready for the fitting of all the half round bars on the rear sides, transom and adjacent to the cod end hatch. I also plan to start trimming the bulwarks, marking out the scuppers and anchor recess and removing the blanks fitted over the steps in the sides of the hull prior to fibreglassing. I also need to fit the plates that support the Kort nozzle and there is also the odd bit of filling and rubbing down to do here and there before the hull can be primed. Should keep me from getting bored for a while, much more interesting than rubbing down fibreglass resin.
I am pondering the possibility of making the anchor and cod end hatch operate as the real thing but have not yet worked out the best way of doing this.
Glad you like the pictures of Shemarah. Goole MBC do still sail on Saturday afternoons from around 1:00 pm onwards and quite a few people go on Wednesday afternoon as well.
Shemarah had her first taste of pond water at the weekend as I carried out some preliminary performance tests. I think I have a good motor and propeller match in the model but I have been slightly apprehensive as its looks so small inside the cavernous hull. The model is a snug fit in the boot of my Jazz but its quite a compact shape and the built in handle makes shifting it reasonably easy.
The model was ballasted to around the expected fully completed weight and the sailing weight on Saturday was 25 Kg or around 56 lb. The short rectangular strips of white tape mark where the design waterline should be (along the bottom edge of the strips).
On the water performance was excellent with plenty of power in reserve.
Manoeuverabilty was very good and the model will turn within about twice its own length at quite low power. I made the rudder about 20% longer chord than scale size as I have found in the past this improves steering ability without detracting from the scale appearance of the model, (and you can always shorten it afterwards if you wish)
There is also adequate thrust in reverse, and the models tracks reasonably straight but there is no significant steering capability from the rudder in reverse.
The motor is a Graupner 900BB torque driving a 75 mm kort prop and nozzle via a 2.1:1 reduction belt drive.
The measured motor input power was 10.85 Volts, 6,5 amps and 71 watts and the prop speed was 2080 rpm which is about 67% of the motor free running speed so its a good balanced and efficient combination.
It was a very encouraging first trial with no need for any propulsion changes. The next step is to make provision for the final, removable lead ballast installation. I added the temporary ballast while the boat was in the water to get the balance correct but I did lift the fully ballasted model out of the pond using its built in handle. However I think making a proportion of the ballast accessible and removable is the way to go.
|Thread: Motor and Prop Survey 2020 Update|
Hello Mark and the other anoraks, here is another interesting combination to add to the database and follows on nicely from the TID above because it details the performance of the Speed 900 transplanted into Shemarah 2 and can be compared with the same motor ungeared
Name Shemarah 2
Type Modern twin rig trawler
Scratch built, mainly ply, plank on frame hull and still a long way to go to completion
Length 1050 mm
Beam 350 mm
Draft 140 mm
Weight Ballasted to 25 kg (somewhere around the expected complete weight)
Motor Graupner Speed 900 BB torque (model number6373)
Propeller size 75 mm in a Kort nozzle (Prop-Shop matched pair)
Reduction gear 2.1:1 using MFA Como Drills belt drive
Battery 12 V 7ah lead acid (all the other batteries in the photo are temporary ballast)
Measured motor performance at full power static in the water was 10.85 Volts, 6.5 amps, 71 watts.
Propeller speed was 2080 rpm which is equivalent to a motor speed of 4368 or 67% of the motor free running speed which is a pretty good match.
The static thrust was measured at between 1800 and 2000 grams.
The photo below shows that perfomance on the water looks good with plenty of power in reserve and the ability to make some really big waves if you are in that sort of mood.
Edited By Gareth Jones on 19/09/2011 09:42:03
|Thread: Shemarah II|
|PS, the other good news is that there did not seem to be any water leaks.|
Well, as the saying goes, 'There is some good news and some bad news'
The good news is Shemarah fitted in the bath and has been ballasted down to within a few mm of the correct waterline, near enough for now anyway. I tested the motor and although its a bit noisier than I would have liked, it seems to provide plenty of thrust. The motor is a Graupner 900 BB Torque driving a 75 mm prop in a Kort nozzle with a belt drive speed reduction of about 2:1. At full throttle the wattmeter indicated that the motor drew 6.4 amps at 11.25 volts with an input power of 75 watts. I will do a more precise set of measurements, including the static thrust, in the pond, where its a bit easier to tether the boat.
However the bad news was that I needed much more ballast than I expected. Heres a picture of the unballasted model.
Here is a picture of the fully ballasted model with all my available lead, 4 additional lead acid batteries, 5 NiCads and an assortment of scrap bits of lead from under my workbench.
When I came to lift the full ballasted model out of the bath to put it on the bathroom scales I thought flipping heck, this feels much heavier than when I tried 7 house bricks and it weighed 45 lb. The scales proved the point as the model weighed near enough 60 lb. At the moment I don't understand the reason for this, maybe Dave Metcalf's figure of 70 lb on the drawing is going to turn out more accurate than Paul Freshney's 43 lb in the magazine article. It looks like some of the ballast will have to be removable and fitted when the boat is in the water. Still it's a bit more progress and weather permitting it will be off to the pond in Goole tomorrow to try out the complete system.
The last couple of days have been spent making the bilge keels. These are not shown on the drawings but can be seen on the photos of Shemarah on the ship lift. I have been fortunate to get some high definition pictures from Kevin Munro via the Trawler Pictures website. One of these shows a square on side view that allowed me to estimate the size and postion of the bilge keels.
I started by attaching a piece of card to the hull using bluetack and masking tape and measuring from its edge to the hull at 20 mm intervals
I then transferred these measurements to the card to get the actual profile of the hull and cut along this line.
I the used this as a template to cut the bilge keel from 1,5 mm ply. I had to trim the edge several times and trial fit the keel to the hull to get a good fit. The keel and hull were both marked to ensure the piece was fitted consistently in the same place.
Four 1/32 holes were drilled in the keel to line up with the frames in the hull and 1/32 brass wire inserted in the keel. To allow the keel to be fitted to the hull, which is curved in 3 dimensions. its necessary to try and ensure all 4 pins are parallell, and the holes in the hull are at the correct angles. The keel was then trimmed to the correct width and length.
Both keels have been trial fitted and given a coat of resin prior to gluing them on with araldite tomorrow.
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