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Member postings for Malcolm Frary

Here is a list of all the postings Malcolm Frary has made in our forums. Click on a thread name to jump to the thread.

Thread: JIF 65
02/07/2021 09:47:11

Almost everything on a model has more than one job, especially the rigging. The primary job of most of it is to stop the mast falling over.

The backstay stops it falling forward in a following wind, but also, when correctly tensioned, affects the shape of the mast and the sails attached to it.

The side stays, if used, keep it upright in a side wind and help keep the mast rigid. Also very useful when launching and retrieving as you can lift the boat by the mast, letting it dangle easily (holding by the mast like it was a frying pan is not recommended). With a deck stepped mast, they also transmit all of the forces from the sails through the hull on their way to the fin, which is shoving the other way.

Some boats have a fore stay, which stops the mast falling backwards. Many (racing types where there isn't room for a forestay) use the fore sail and its associated lines to do the job. There is a line running down the leading edge of the sail (which is tensioned to this support line) to the front end of the boom, the boom itself, and a swivel or bit of line from a point on the boom to the deck. Some get a leech line, which starts somewhere near the top of the sail and goes to the rear end of the boom. This completes the triangle and allows the fore sail to be properly shaped without being unduly tensioned.

My version of keel stepping doesn't allow for adjustment, if I need to alter things to get a better balance, I need to do something radicle with sails. A deck plate allows for adjustment.

A gram saved at the upper end of the mast is ounce saved down below, since the weight down at the bottom doesn't have to counterbalance as much weight at the top to provide the righting moment. Since both DF65 and JIF are intended to conform to the same racing rules, there will not be huge differences between the two sets of sails, and, being of very similar area, will generate very similar forces. Of course, cut, shape and material will make differences, as will their eventual fitting and adjustment.

Thread: 2021 Builds during lockdowns
30/06/2021 09:46:23

Just guessing, but I have a feeling that the original builder had some misconceptions about rigging a yacht which might have contributed to the abandonment of the project. Some closer pictures of the sails might help confirm or deny.

As a general rule, the leading edge should be arranged to be straight, the trailing edge left to find its shape. On most swing rigs the fore sail has its own boom rather than being loose footed, and, just like any other yacht, there is a "slot" between the trailing edge of the fore and the mast.

Thread: Todays Boating
27/06/2021 09:32:39

Way back when I was incarcerated in a control office I asked one of my merry men what it was like on the moors above Littleborough. He said, and I quote, "Still snowing from last year".

26/06/2021 20:23:35
Posted by Paul T on 26/06/2021 17:52:26:

Ashley

The weather is getting bad in your area, watch out for storms and icebergs coming in from the Heron Lake.

Meanwhile it so hot up here int north that the cobbles on the M6 are cracking

Paul

Surely you mean the M62 where patrons of the highway are allowed to avoid both Oldham and Rochdale in one go?

Thread: JIF 65
25/06/2021 10:07:11

My thoughts are turning to servos, I will use a drum drive as the arm alternative causes the thread to move through a linear quadrant or arc (whatever), with variable torque to the rudder arm. I can now see that the drum has the thread moving along a constant path, the torque applied is consistent and finally I can keep the hole through which it passes quite small. Still do not know what brands are wort considering, or how powerful a servo is needed for the rudder.

Do some measuring. Determine the distance from the boom connection point to the deck connection point both when fully "in" and "out". The difference is the needed travel. The drum is approx 1" diameter, 3 and a bit inches per turn. A 2 turn winch will do the job, DF65 uses , I believe, a 1.5 turn winch. A bit of extra travel lets you be a bit sloppier in line layout. I prefer winches for their simplicity in installation in a confined space, but an arc, properly arranged and with a sufficiently high torque servo, uses the variable torque to advantage. Probably the King Max 2 turn metal geared one.

For the rudder link, swinging the rod through an arc is no problem - just make the hole oval. The speed lads use rubber bellows to cover the hole. Simple, cheap, works. Rudder servo? Look in the DF65, observe the mini servo, get a similar one with metal gears.

Given that the boating lake near here is saltwater, I am not at all sure that Brass is the best, nor is the steel, chrome plated any better. I would use Stainless steel, also knowing that this is prone to Chloride attack. I guess that a good wash down is needed for all the options.

Brass. As simple as that. Stainless steel if that is needed for strength. Chrome plated steel is a disaster in a hurry to happen, chromed brass or stainless, OK. Lacquer is good.

None of my boats have ever used a deck plate for the mast. Wherever possible, they are keel stepped and sit in a brass tube that goes from deck to keel (meaning hull bottom in this case, not the lump on the end of the fin) and is an integral part of the rigidity of the whole thing under load, avoiding putting any undue stress on the hull structure.

A bit of extra weight in the rudder will probably be offset by the weight of water that it displaces, but a lightweight rudder "might" provide a bit of buoyancy at the stern, which might be a factor in the performance of the original.  Having a rudder that is not quite as strong as its mount is no bad thing.  Careful handling is no bad thing, but a broken rudder is much easier to fix than a broken hull.

Edited By Malcolm Frary on 25/06/2021 10:10:22

Thread: Suppressors when using 2.4gHz?
15/06/2021 14:59:28

As a brushed motor rotates, each brush shorts out one of the windings as it passes from one segment of the commutator to the next. All of the energy stored in that bit of the armature wants to go somewhere, and that puts a lot of current through the bit of brush doing the shorting. The suddenly changing field that this causes also appears as stray voltage spikes at the motor terminals which send current p the motor leads. It is this current that generates the interfering signal rather than the spark itself, the spark is a visible thing that indicates that something is happening.

Bits of muck and uneven-ness on the commutator allow the sparking to continue for more of the rotation time, thus a tired motor (or one that was designed tired) generates more interference.

Thread: Which prop shaft
15/06/2021 09:20:46

Probably the project in his other thread.

Thread: What's the foresail on a cutter-rigged ketch called?
14/06/2021 16:16:57

Spotted on https://www.sailboat-cruising.com/cutter-rig-sailboat.html - it "might" be what the writer on there referred to as a "Yankee". This might mean that that particular sail has different names in every area where it is used.

Thread: Swordfish, Jetex & Ashley's Article July 2021 Model Boats
13/06/2021 10:46:17

A lot of years ago one of my less stable workmates got a rocket kit by "Estes". Entertaining if somewhat scary, use involved an electric firing device (basically a filament bulb with no glass envelope and a long piece of wire). The motors/fuel still seem to be available after a quick web search.

Thread: Todays Boating
06/06/2021 09:24:50
Posted by ashley needham on 05/06/2021 19:39:28:

...but more importantly....

i have an 8 inch length of 4mm st/st rod and it’s bent. Not bent bent, but there is the slightest wobble and it won’t do at 20,000 rpm. How to get it dead straight?. (No lathe),,

ALSO...the elastic on the Diamond has gone really saggy on yer masts. Disappointing after only a few months. I might buy more and try again , perhaps it was an old batch?

Tomorrow. Fishy. Stingray, specials and a lander.

Ashley

An unwanted curve might respond to the old telephone engineers technique of stroking relay springs into shape by stroking the the curve out. Only a lot bigger. Clamp the rod so that the curve is in a known direction, use a bending crowbar (nice strong metal bar with a couple of bolts about 1" apart at one end to go each side of the rod, gently stroke along the length of the rod against the curve. Repeat until satisfied that the curve has gone.

Thin elastic has its disadvantages. If tight enough to look straight, it will lose its elasticity fairly rapidly. If not under tension, it will sag. OTOH, a 75 metre bobbin of shirring elastic from the haberdashererer was cheap enough many years ago.

Thread: Suppressors when using 2.4gHz?
04/06/2021 23:28:34

While the radio will not pick up any interference through its aerial, it will quite happily be affected by any stray voltages offered via the power. All RC depends implicitly on stable voltages to drive the voltage comparators that everything uses to get the timing pules right. A capacitor across the motor terminals will soak that source up nicely, I remain to be convinced that the other two do anything in practice as opposed to theory.

An unsuppressed motor is unlikely to generate radio frequency that will upset 2G4 radios. On the other hand, there is the outside chance that a model cheerfully transmitting motor noise might sail near to one running 27MHz, and provide a viable signal for that. The result, seeing that steering is invariably on channel 1, would be poor steering on the 27MHz boat. (Might be true of some 40MHz as well). So suppression is also good manners.

Thread: JIF 65
03/06/2021 09:33:55

A square edge at a transom works very well because once the hull is going fast enough the grip of the water is broken. Normally, this only applies to powered hulls. Underwater, a different story. Air is not replacing the turbulent water at the back edge of the fin, but water is being pulled into what would otherwise be a void. Creating turbulence like this takes energy, and appears as drag.

Commercial racing fins are sharp enough on larger models (e.g. IOMs) to make use of gardening gloves advisable when carrying the boat. My home made efforts in ply usually have a small radius, either because I sanded them that way, or because in one case I took it to an edge and carrying it over time wore it to a radius. Edge vs radius showed no noticeable difference for cruising, so a bit of effort (say 5 minutes with a power sander) creating the taper, will pay dividends when you want to steer the boat later.

The bulb plot is sound.  The entire bulb will presumably get a layer of epoxy or similar to ensure that it has a watertight skin so that the bolts never get wet.  Even so, investing in stainless or brass bolts might be a good idea.

Edited By Malcolm Frary on 03/06/2021 09:38:43

Thread: Names of paint colours...?
01/06/2021 21:46:19

It looks like a post war ship, possibly 1950's, so white outside with a selection of browns inside would look to be legit, or legit enough. Not having a true back story, it is ripe to gain one, which could include a lot of trading or ferrying in distant backwaters of the far east.

Thread: Futaba RX power & battery type
17/05/2021 11:33:20

A LiFe cell has a nominal voltage of 3.3, so 2 of gets 6.6 volts. I would be cautious about using LiPo cells, the seemingly small increase in voltage might not be good for the electronics.

One of the most common queries for DF65s was " do I have to replace my dead steering servo with a Joysway one or can I use something costing less". This was usually from users who had maxed on the battery voltage.

Dry batteries are normally single use non rechargeable types and are suitable for low drain applications, but are incapable of supplying high currents and maintaining their voltage. Rechargeable batteries are to all intents and appearances as dry as anything else, but inside are as wet as so called dry batteries. They do have the merit of delivering heavier current while maintaining their voltage.

"Dry", when applied to batteries just means that you can't pour the wet stuff out, as opposed to leclanche cells that could be re-enlivened by dropping a few sal ammoniac tablets into the visible liquid, and repeated until the electrodes dropped to bits. Just a case of the wrong words from past technology sticking.

Thread: Simplifying charging
14/05/2021 10:42:12

To work as required, a change-over switch is required between the battery and ESC. With two batteries and ESCs, this is either two switches or a "DPDT" switch. The important parameter is the current carrying ability of the switch, which needs to be high enough for the anticipated load.

There are equipment sockets that have a switch built in, but these are usually only intended for low currents, usually too low for the motor current, which is the important consideration.. Picking one to suit the 5mm plug section of a battery eliminator "spider" would probably be easiest to handle later. Such plugs are available, and can be fitted to the charger lead. Charging both from on socket would require a rectifier diode between the socket and each battery lead to avoid one battery trying to charge or discharge the other. Or two sockets, and two chargers. Or two sockets, one charger, and remember to actually plug in and charge both batteries.

A pair of battery extension leads with Tamiya male at one end and female at the other could be cut into to insert the switch and plug without any alterations to the batteries or ESCs.

Much like Richard said while I was typing.

Edited By Malcolm Frary on 14/05/2021 10:44:26

Thread: Two Brushed motors and 1 ESC
12/05/2021 17:38:20

SLA are usually quoted at their "10 hour" rate. So in theory a 12AH battery can give 1.2A for 10 hours. As Charles mentions, pulling 12A will not give a 1 hour run time, in the real world, under 1/2 hour. And that is assuming one in top condition.

A member of my club, many years ago, built a lifeboat model and, because it was all he had experience of, ran it on a 12 volt SLA. It chugged around like a tug, had a short run time and a hot motor. Changing to a "7.2 volt race pack" transformed it. It was able to semi plane and ran longer. Less weight, battery able to sustain the load.

Edited By Malcolm Frary on 12/05/2021 17:39:46

12/05/2021 09:42:40

While the ESC might be happy providing the current that the motors want, the battery might not. Lead acid bricks, even fully charged ones, are good for providing low levels of power over a long run time and ballast. They can only support high currents briefly. NiMH or LiPo does a much better job with continuous high current.

Lead acid were only in common use because back in the day they were almost the only game in town. When alternatives became easily available, their use declined, but old designs and their associated specifications were never updated.

Thread: Todays Boating
10/05/2021 10:33:58

Ribble MBC use a floating cross for their tug football. Much easier to push around than a circular object since it has corners rather than a continuous slide-off surface. Vicious tackles are also possible, if not mandatory. Use in a shallow pool is advisable, since sinkings are also part of the deal.

Someone may have posted a YouTube video of their goings on from the various shows that they attended.

Thread: Identification
04/05/2021 09:50:25

The length indicates a Marblehead, which is really a race boat. The presence of handrails and the deck hatches and cockpit says otherwise. As does the combination of a pond yacht fin with a spade rudder separated by a distance from the fin.

Over the years 'I've seen a few yacht hulls in shop windows. The trade of the shop never had anything to do with yachts, real or model, and if rigged, never looked like they could work. But they were eye catching. This one might have had a similar original intention.

Real Club Nautico Gandia might have been having a reception area clear-out.

Edited By Malcolm Frary on 04/05/2021 09:56:05

03/05/2021 08:30:49

6 1/2 inches draft and under 5 pounds weight indicates a shelf queen rather than a worker. Any screw holes in the deck could give a clue as to what fittings may have been carried.

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We welcome well written contributions from Website members on almost any aspect of Model Boating with a particular emphasis on practical hints, tips, experience and builds.

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