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: Prop shaft vibration|
A single 'universal joint' coupling can only accommodate angular misalignment between the input and output shafts. It cannot accommodate any lateral offset, i.e. side to side or up and down misalignment of the shafts. A pair of couplings can accommodate lateral offset as well, the amount of offset being dependent on the length of the shaft between the couplings. However with a double universal joint, the couplings act as the locating bearings for the centre section of shaft. If there is any play in these bearings the centre section of shaft is liable to vibrate.
The geometry of universal joints is complex and subtle. For example many joints are not constant velocity, i,e, if the input shaft is rotating at constant speed, the output shaft will rotate at a speed which varies with angular position as the coupling rotates. This can lead to noise, vibration and wear. Obviously these effects are more significant with systems that are transmitting high powers at high speeds.
If at all possible its best to arrange the propshaft in your boat to be as straight as possible with the absolute minimum offset and angular misalignment.
|Thread: Snogg the sequel|
Sorry but I made a mistake in my post on the 17th, the normal motor in the Springer is now D3536-9 which is the same diameter as the proposed PT boat motor but about 12 mm shorter.
I did use a D2836-11 for a while and it was OK and safer as a have a go boat but a bit underpowered for fun sailing.
Sorry for the confusion, I had too many motors sitting on the bench when I was swapping things around.
Its difficult to provide the whole picture on the forum as there is no easy way I know of to display an Excel spreadsheet. If you would like a copy of the complete sheet with all the data I have collected, send me a PM with your email address and I will forward it to you. However a summary of the Springer data is as follows.
Graupner Speed 500E brushed motor, 7.2V NiMh 40 mm 3 blade prop driven at 3250 rpm (45% of unloaded speed) max load current 4.1 amps, This was the original configuration I used for the model, worked OK but a bit slow and the motor got hot with prolonged running at high power.
Turnigy D2836-8 1100KV brushless motor, 7.2 V NiMh 40 mm 3 blade prop driven at 5900 rpm (70% of unloaded speed) max current 12.2 amps. Not sailed in this configuration
Turnigy D2836-11 750 KV brushless motor 7,2 V NiMh 40 mm 3 blade prop driven at 4685 rpm (82% of unloaded speed) max current 5.5 amps.
Turnigy D3536-9 910 KV brushless motor 7.2 V NiMh 40 mm 3 blade prop driven at 5710 rpm (80% of unloaded speed) max current 9.9 amps. Standard working configuration now, also used with 11.1 V LiPo occasionally
Turnigy D3536-9 910 KV brushless motor 11.1 V LiPo 30 mm 3 blade prop driven at 10740 rpm (89% of unloaded speed) max current 9.4 amps Not sailed in this configuration
Turnigy D3548-4 1100 KV brushless motor 11.1 V LiPo, 40 mm 3 blade prop driven at 9540 rpm (76% of unloaded speed) max current 35.1 amps Not sailed in this configuration
Turnigy D3548-4 1100 KV brushless motor 11.1 V LiPo, 30 mm 3 bladed prop driven at 11630 rpm (89% pf unloaded speed) max current 17.5 amps Not sailed in this configuration
As a guide I work on the basis that provided the max loaded speed is at least 75% of the unloaded speed there is a good match of motor and propeller. Between 45 and 75% the combination is usable with care, i.e. provided the model does not need to spend long periods at high powers, eg a model narrow boat. Below 45% the motor is running too inefficiently and will quickly overheat if high powers are used.
I have sailed the Springer with a D3548-6 790 KV brushless motor on an 11.1 V LiPo but not measured its performance. However I did produce a rather blurred video of its performance and there is a link here supercharged springer
That's an interesting point about the drag from the un-driven centre propeller. Intuitively I would have thought that a fixed pitch propeller that was allowed to spin and 'freewheel' would create less drag than one that was held static. However I could be wrong. On another forum that I often frequent (PPRuNe) there was recently a similar debate about whether a seized turbofan engine would create more or less drag than a windmilling one. Opinions were mixed but there was some old flight test evidence that suggested a seized turbojet engine did create more drag than a windmilling one at high speeds. Since I spent over 40 years as an aircraft flight systems engineer, much of it working on the aircraft in question in the PPRuNe debate, I suppose I should know the answer. Unfortunately I don't. I think I know a man who worked at Rolls Royce Bristol who would know the answer but I suspect that he, like me, has been retired for some time - John Bewick, where are you now?
On Snogg in its previous incarnation the centre propshaft and propeller were allowed to freewheel and the overall performance was OK. Whether, and how fast the propeller rotated I have no idea. On the rebuilt model it would be relatively easy to try all three options, fixed, free and no centre propeller and see if there is a discernible difference. It would be easy to leave the centre propeller loosely threaded on the shaft for display purposes and remove it when sailing and that should clearly give the lowest drag. However it would be only a matter of time before I forgot to remove it or tighten it before sailing and lost it in the oggin. I will report back with some test results when the model is tested some time next year.
I should perhaps have added that although the original PT boats had three engines, Snogg the model will just have two motors driving the outboard shafts. The centre shaft and propeller will just freewheel for scale purposes. In the models latest incarnation the centre shaft will be much shorter and not extend fully into the hull as before, This will give me the option of laying the battery along the centreline of the hull rather than across as before.
Dave, thanks for the information about your Huntress. I think Snogg will be quite a bit heavier and draggier than the Huntress so it is likely to need more power.
Alas my snogging sessions have also suffered a marked decline over the years.
Edited By Gareth Jones on 17/12/2019 19:28:48
You are not paying attention, I explained this to Dave Milbourn a short time ago, admittedly in another thread.
The model is finished as a Royal Norwegian Navy vessel, originally build number PT602, which was built in 1945 for the USN or possibly the Marines, but did not see service in WW2. After the war it was sold/transferred to the Royal Norwegian Navy under a weapons aid program and was named Snogg, which is Norwegian for fast. Snogg was the first boat in that batch which were known to the RNoN as the Elco class.
Subsequently the RNoN have had several other batches of PT boats, several individuals named Snogg and from 1970 there was a batch known as the Snogg class.
The thread is called 'Snogg the sequel' because it follows on from the original article.
To bring the thread up to date the next step was to carry out a performance test with the proposed brushless motor. For many years we have had two Springers that have served us well as test beds and also have a go boats. One of these was sold at the last Blackpool model show but the other has been retained as a test bed and boat of choice for the Manx model boat club's hooligan competition at their Manannan event. It is normally powered by a D2836/11 motor (750 KV) which drives a 40 mm prop and gives quite a spritely performance but not PT boat speeds.
The chosen motor D3548/4 is a bigger diameter, but fits on the same mount and is an easy swap, just moved forward by about 12 mm. The installation was fitted up with my wattmeter and it was off to the bath to test it.
Driving the existing Springer 3 bladed 40 mm prop and using a 3 cell 6000 MaH LiPo battery, the motor gave me a prop speed of 9540 rpm and took 34 amps. This is above the rating of the speed controller which is a 30 amp Leopard unit. However it was OK for a quick test and survived unscathed. I have not got any photos taken during the test as it takes one hand to hold the boat steady, one to hold the tacho to read the prop speed and another pair of hands to operate the transmitter.
Driving the 30 mm PT boat propeller the brushless motor gave 11600 rpm with a current of 17.5 amps. By comparison with the original 700 sized brushed motor this is about 2% increase in prop speed but with only 73% of the current consumption and only 40% of the weight. Overall it looks a promising combination and I can now go ahead and design the mounts for the motor and the new propshaft and P bracket installation. I will probably replace the 30 mm props, which I think are standard Raboesch units, with some similar sized Prop Shop propellers which are a more accurate representation of the full sized ones. If necessary I could go up to 35 mm diameter without greatly compromising the scale appearance and still be within the 30 am speed controller rating.
Edited By Gareth Jones on 17/12/2019 18:03:00
Why bother removing the propshafts you may ask? Well there were several reasons. The drive shafts themselves had been lengthened to 420 mm to provide the required clearance to fit the 700 sized motors. This put the motors and overall boat centre of gravity further forward than ideal. The replacement motors are smaller and lighter and I wanted to install them further back.
The boat is fitted with 30 mm diameter 3 bladed propellers which are a good scale approximation to the real things which were 28 inches diameter. I have made many detailed performance measurements on the model and I know that I need around 11000 rpm with the 30 mm props to give good boat performance. However the installation was susceptible to vibration and probably some whirling of the propshafts so shorter shafts were desirable.
Finally the real boat has exposed drive shafts outside the hull, supported on P brackets, and I wanted to make the model more representative of the real thing.
Based on my experience with other brushless motors I had decided that a Turnigy D3548 sized motor should be powerful enough and the 1100 KV variant should give a fast enough prop speed. I might go up a small amount in prop size to 35 mm but even so this motor should perform OK. As a comparison the two motors are shown below. Note the brushless one is a lower KV but the same physical size as the one I plan to use.
As a comparison, the brushed motor weighs 390 grammes, the brushless motor 160 grammes. Both have 5 mm diameter driveshafts.
Some of you may remember an article I wrote for the magazine about 10 years ago, covering a major rebuild of a 1:24 scale model of an ELCO 80 ft PT boat. The article is still on the website and there is a link to it here PT 602
I have now started a second major rebuild and this is the first of an occasional look at what I am doing, As described in the article the original rebuild had a long string of propulsion problems, mainly due to my inexperience at the time, Eventually Snogg did achieve a good performance on a pair of Speed 600 motors as shown below.
Subsequently the model was fitted with a pair of Speed 700 motors (Graupner part no 7307) which ran much cooler.
Here is a picture of the Snogg internals as they were with the later motors and NiMh batteries.
Subsequently there was another weight saving exercise and a 6000 MAh 3 cell LiPo battery was used instead.
However time has moved on and the model was always ripe for a brushless conversion. There are also a large number of other potential improvements I would like to make adding more detailing and hopefully working roll off racks and torpedoes. However the first step has been to strip out all the internals and remove all the deck fittings so Snogg has now been gutted.
Everything came off OK without any damage but removing the propshafts was a bit of a challenge. I made up a wooden block drilled out 8 mm to be clamped around each propshaft with a pair of molegrips.
The prop shaft was then heated with a small blowtorch to soften the araldite holding it in the hull, being careful not to set the hull alight. A bit of twisting with the molegrips and all three propshafts were removed successfully.
A bit of cleaning up is required but so far so good.
|Thread: Spektrum MR200 receiver question|
Thanks for a very quick and helpful response. I will give it a go and cut back the screen accordingly. I have measured another receiver antenna and it is 31.2 mm long as best I can tell. I think I will put a length of heat shrink over the whole length of both antennas as the step where the screen is cut back does create a weak spot which flexes and eventually cracks the conductor. I will do a range test afterwards.
Edited By Gareth Jones on 17/12/2019 15:31:47
I have a Spektrum MR200 receiver which has worked faultlessly in a number of models. However as a result of multiple swaps between models the last inch or so of one of the two antenna leads has broken off. As I understand it, this last inch of un-screened wire is the antenna, the rest of the grey covered wire is effectively an extension lead.
Can I cut back this broken wire to reveal a similar length of un-screened wire to act as a new antenna or do I have to replace the whole antenna wire (assuming its possible to get one) ? If I can cut the wire back to make a new antenna how critical is it that I get the right length?
Any advice gratefully received.
|Thread: Kingston Peridot|
East Riding archives had a project to digitise many of the drawings of the Cook, Welton and Gemmell shipyard in Beverley where Kingston Peridot was built. They have a website called Trawling through time which gives a lot of information about the project and there is a link to it here Trawling through time
Kingston Peridot is one of the examples they show on the website and there is a link to the drawing here Kingston Peridot. I don't know if there is enough information for you on that drawing but there may be others or drawings of other similar vessels built around that time you could have a look at. You might need to contact or visit the archive centre at the Treasure House in Beverley to find out whats available or you may be able to search the records on line.
If anyone is thinking of building a model of a Hull (or Fleetwood) trawler I am sure there would be lots of interesting and useful information available on the Trawling through time website.
|Thread: GBR 59|
The convention for sail numbers is for registered yachts to carry the last two digits of their class registration number on the sails. However there is no guarantee that the sails you have were the original ones. If the yacht was ever registered it should have an MYA registration number, usually 4 digits, clearly marked inside the hull either by painting, bonding or moulding in. The number should also be marked on the outside of the hull, usually on the deck, but there is no requirement for these external markings to be indelible. If you can find the number you could try contacting the IOM class registrar to see if the original certificate can be traced. Contact details are on the MYA website.
Unfortunately I am not an expert on IOM designs and they all look much the same to me so I can't identify the design of your yacht.
|Thread: Shemarah II|
Snogg was the subject of a magazine article some years ago and the last time I looked it was somewhere on this site, I am sure Colin knows where it is. The model is an Elco 80 ft PT boat, build no PT602, surplus to USN requirements and supplied to the Norwegian Navy at the end of the war as the first of the Snogg class. Snogg is Norwegian for fast.
This will probably be the epilogue of the Shemarah thread. A couple of months ago Elizabeth and I visited the vast Richard Howard collection of model boats at Beale Park near Reading. It was an open day for potential buyers but we not really tempted by anything despite the huge variety of boats on offer. However it did bring home to us that we really should do something to downsize our collection of about 30 model boats and yachts, about half of which rarely get sailed. We therefore decided that we would begin to sell off some of our collection, if only to make way for potential future projects.
Coincidentally, about a week later I received an email from Donald Moodie, the master of the full sized Shemarah II, asking if I would be interested in selling my model to him, as in his words 'Shemarah has been a large part of my working life and to have such a fantastic model would be a dream come true' Shemarah has also been a large part of my modelling life but it could not go to a more deserving home, much better than it spending years sitting in its box in our shed. It had its final model show outing at Blackpool last month and its last local outing to the York MBC night sail event before being checked out ready for collection.
Donald came down to collect it yesterday and it is now in the home of his father, Peter Moodie, who commissioned Shemarah II from the Campbeltown shipyard for the Moodie family business in 1996. When he rang me to express his delight at having the model he sounded as excited as Donald was when he collected it. They had already tested it out in the family bath within a couple of hours of getting back to Scotland. The picture below shows Donald collecting the model from our workshop yesterday.
The workshop is now clear for my next project which is to be a major refurbishment of Snogg, my 1:24 scale model of an 80 ft Elco PT boat that I originally refurbished about 10 years ago. This time it is going to get a brushless conversion, working roll off racks and torpedoes and much more scale detail. I might start a new thread on the project once it gets underway properly, probably after Xmas.
|Thread: 36R model yacht information|
This is an update on progress on the build of my 36R model yacht.
After some thought I have made a keel to one of the designs suggested on the American Model Yachting Association website. It consists of a 1/32 ply core sandwiched between two pieces of 3/32 balsa. This was sanded to shape and then covered in two layers of unidirectional carbon fibre cloth followed by a single layer of woven carbon fibre cloth. Each layer of cloth was separately coated in Z-poxy resin before adding the next. The resulting keel seems pretty stiff.
I have made two supporting frames from 4 mm liteply which tie the keel to the sides of the hull and added a longitudinal stringer at deck level. All the parts interlock so the keel is very rigidly located and supported.
The rudder skeg was made from 4 mm ply covered in glass cloth and also locates in the longitudinal stringer. The rudder is of similar construction with a brass tube keyed to the rudder with three 1/16 brass rods as a pintle.
I made a stand which supports the hull with the waterline horizontal and the hull laterally level so that I could check the keel and skeg are both vertical and in line. The stand is just a couple of scrap pieces of 9 mm MDF, supported on a magnetic working board.
After sanding down and drilling some lightening holes the whole assembly has been glued together with Araldite. I have added a small ply plate to form the basis of the mast step.
My next task was to cut a slot in the lead keel weight to take the bottom of the fin. I worked out the C of G of the keel weight by balancing it on a round piece of dowel. I have a drawing of a similar 36R hull which showed the centre of buoyancy of the hull and assumed for the time being this is the same on my hull. I then marked the position of the slot in the ballast weight so that its Cof G will be directly below the hulls C of B.
After marking the required position of the slot I chain drilled a series of 6 mm holes about 30 mm into the ballast weight. I then fixed the ballast weight on to my workmate and using a 6 mm cutter in my router, cleaned up the slot to the full length and depth, gradually increasing the depth of cut by a couple of mm each time. This gave me a nice clean slot with no apparent damage to the cutter or router. (I carefully swept up all the bits of lead afterwards)
I have made the deck from 2 mm liteply with cutouts that will be covered in adhesive deck patches to give access to the interior and reduce weight. The deck has been given a couple of coats of Z-poxy to seal the surface but needs to be rubbed down and will be given a final coat of varnish after its glued on.
I made a mount for the vane mechanism from a piece of 1 inch wide carbon fibre strip that I found in my new desk during an office move about 30 years ago. I knew it would come in useful one day. Its very light and very stiff.
I have estimated the weight of the mast, sails and rest of the rig by weighing a Marblehead rig I have and assuming the 36R will be about 90% of the weight. A tin of salmon and packet of Oxo came close to the estimate at about 420 grms.
Next came the first bath test with the keel weight held on the bottom of the keel with tape.
Miraculously everything seems in balance so my next job is to fix the keel weight permanently
A bit more progress to report shortly.
|Thread: Spider J|
You are all too kind with your comments, it's not really that good.
Here are a few photos of Humber Princess taken at Silverdale Glen on the Isle of Man following this years Manannan Model Boat Festival organised by the Manx Model Boat Club. It looks to me that I need to make a minor change to the ballast distribution as the model is sitting slightly 'down at the head,' I believe keels and sloops were typically sailed that way so that if they ran aground on the shifting sand and mud banks of the Humber they were easier to refloat. However I plan to remove a bit of the forward fixed ballast block to level up the hull when in the water.
You may notice that the cog boat is conspicuous by its absence. Sailing with the cog boat tied to the stern revealed it was easy to swamp the boat with a quick burst of power from the propeller and we spent about half an hour afterwards trying to retrieve the oar which had drifted off on its own. However the cog boat stayed firmly attached to the sloop and was easily retrieved. Maybe it will have to be a static display only item.
Spider T is now effectively complete and as near as makes no matter finished. The only remaining tasks are to do a bit more weathering to make it look slightly more used and add a second crew member when I find a suitable subject. Here are a few photos taken this morning. I will add a few sailing photos when I get the opportunity to do some sailing, hopefully this coming weekend.
What next, I hear you ask Ray. Well the long term plan is still to build a similar size and scale model of a wooden hulled Humber keel, but before I start that I am going to have a bit of a change.
I have a fibreglass hulled 36R yacht to build as a vane steered variant, still at the planning stage, although I have the hull and keel weight.
Next month we are expecting to get a bare fibreglass A class hull of a John Lewis design called Challenge to add to our collection of vintage racing yachts. That will be a bigger job as I will need to make a keel weight pattern and get it cast using around 42 lbs of lead.
I have a 1:24 scale model of an Elco PT boat that needs refurbishing and it will probably get a brushless conversion as it is missing both speed controllers. I also plan to add a lot more fine detail to the deck and superstructure.
I have also been given a plan and fibreglass hull for a 1:24 scale German S boat which will complement the PT boat well, but its probably a 3 or 4 year project. I was also very kindly given a whole series of supporting books, along with the hull by Peter Robinson so it should be given a fairly high priority really.
We have several other yacht refurbishments on the go and I am currently adding the control gear to a model of an International Dragon that Elizabeth is building in the style of Bluebottle, originally, maybe still, owned by the Duke of Edinburgh. There are also three Marbleheads in the loft (one of them built by Bob Abell) that all need major refurbishment so I am not going to be short of work over the next few years.
The cog boat is now ready for staining, varnishing and painting.
Spider T is now pretty well complete and I will post some photos if it ever stops raining. There are a few minor details still to add and a bit of weathering to do but it should be finished by the end of next month at the latest. Elizabeth is making the fenders at the rate of about 1 a night so they will be added this weekend.
The major task over the last few weeks has been the completion of the cog boat. I started this a few months ago but was not impressed by its looks. The planks were too narrow and too thick so I ended up abandoning that one and starting again, this time with 10 mm x 1,5 mm lime planks in lieu of 8 x 2. I am really pleased with the way this Mk 2 cog boat has come out and the only remaining parts to make are the knees and oar for sculling over the stern.
Here is a view of the planked hull on its building jig.
The next picture shows the inside of the hull.
Here the gunwhales have been added and the start of the ribs, I think the ribs are slightly on the thick side but look to be about the right spacing at a scale dimension of about 6 inches.
Here is the fully ribbed hull
And now I have added the floor beams and floor planks
Currently I have fitted the seats but still have the knees to fit in the various corners,
After that its varnishing and painting. I plan to do the outside of the hull in black with a red stripe along the top plank. The inside of the hull will be varnished. Typically cog boats were finished with a tarred hull inside and out. The single oar for sculling over the transom is part finished, awaiting the glue attaching the paddle to the shaft to dry.
All this woodwork has re-awakened the thought of building a wooden hulled Humber keel next, but who knows?
Edited By Gareth Jones on 19/06/2019 10:13:29
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