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Now here's a question for the experts. I have two identical waterjets for fitting into a model; same size and same rotation for forward motion. Will I see the same effect as if I had two open water props which were the same? Roy
Inwards or outwards - should the props be turning to meet together above the shaft or below it? Also from Wikipedia "Contra-rotating is where parts of a mechanism rotate in opposite directions about a common axis, usually to minimise the effect of torque. Contra-rotating propellers should not be confused with counter-rotating propellers, a term which describes non-coaxial propellers on separate shafts; one turning clockwise and the other counter-clockwise." Torpedoes are a marine example of contra-rotating props. Roy
I should clarify my comment about 'no sanding' since it's not all 'plain sailing'. The first coat goes on easily and did not, and should not, require any sanding. For the second and subsequent coats, the fibreglass is essentially smooth and does not hold the resin in place so well. So these coats will be fine on a horizontal surface, but on a slope the resin will tend to run, and overlap on a hard edge. If you can ensure that you don't apply too much resin it's fine, but if you get runs, you'll have to sand.
Having now completed fibreglassing a hull using the method shown in the video mentioned earlier, I can say that this has been, by far, the most satisfactory fibreglassing I have attempted. A smooth hard finish with no bubbles, no ripples, and no sanding. So for anyone who has been struggling using the technique of undiluted resin and credit card spreaders, I can thoroughly recommend the video'd method. Roy
I have read on this forum and others that fibreglass has no strength and am puzzled by these comments. Fibreglass is commonly used for building the hulls of full-size boats, including lifeboats, which implies that it has considerable strength. Admittedly, their hull walls are much thicker than on a model boat, but the strength is there. I have seen a fellow model boater take a hull made of balsa, which had been coated with fibreglass and bang it on the edge of a table, with no damage. As we all know, you can poke a finger through untreated balsa. Finally, some data is provided on wikipedia that fibreglass impregnated with polyester resin has a tensile strength of 8000 pounds per square inch. So some clarification of the 'no strength' comments would be appreciated. Roy
Some can do fibreglassing as easily as shelling peas. I have fibreglassed 3 models so far and have yet to master the technique. I've spent far too much time sanding the results to make them smooth. For my next project I plan to follow the guidance shown here:https://www.youtube.com/w atch?v=ujk-wBQDUSk. He talks about 'denatured alchohol' which, in the rest of the English-speaking world is referred to as methylated spirits.
I was able to test the new paddle wheels on the water today and they have proved to be the solution to the old wheels digging in. She no longer develops a list when under way. The other advantage is that there's no longer a big wave from the paddles, and it's possible to get up to a realistic maximum speed. Hope to have some video to post in the near future.
Screw holes for holding the support beam in position were marked in the sponson supports and drilled. At this point the assembly could be installed permanently. - Removed the nut and washer from the centre of the master rod and attached the support beam to it; replaced and tightened the lock washer and nut. - Slid the wheel onto the shaft until the locating holes for the support beam lined up with the screw holes in the sponson supports and fitted the screws. - Final check of rotation on the shaft.(see video) - Tightened the wheel drive collar onto the paddle shaft. This was a 3/16” collar drilled for a short length of 1/16” brass rod, which was soldered in and then bent to fit into one of the drive holes near the centre of the inner side wheel. The video shows the motion for the starboard wheel. It has been operated under radio control, but even at its lowest speed it goes too fast unloaded to see the motion clearly. All that is required now is some liquid water to try it out and learn whether the objective has been achieved.
I will be interested to learn how your electronic solution to speed control and steering works. I have not run my model at full speed because the paddle wheel throws up quite a wave behind it and would throw a lot of water onto the aft deck. I typically operate the paddles independently to try and minimise the list, and use the rudder for steering. Roy
A beam was needed to support the pivot for the feathering mechanism. It was made to straddle the gap between the two sponson supports. There’s even less information available about this than there was for the feathering mechanism. My second attempt was the best solution and comprised the following parts. - Two 3/8” lengths of ¼” brass angle; with a clearance hole drilled in the top flange near one end, to suit the small sheet metal screws I had on hand - A length of 1/8” x ¼” rectangular brass tube to span the gap between the sponsons. - Approx 2” length of ¼” x 0.030” thick brass strip - A ½” length of ½” wide by 0.030”thick brass strip - A 7mm length of 3/16” brass tube as a bushing for the pivot. The rectangular tube was cut to length to fit across the sponson supports and inside the paddle boxes. The two pieces of ¼” angle were soldered at right angles under the ends of the 1/8” x ¼” tube. The paddle wheel and the beam were placed in position. The paddle wheel was set up while stationary to position the paddles so that one was on bottom dead centre and vertical. The axial position of the pivot point centre was marked on the beam, and the distance below the edge of the beam measured. The top edge of the ½” square strip was intended to be flush with the top of the beam, and a 3/16” hole was drilled through the former at the pivot point centre. This was soldered to the ¼” wide brass strip, and then the 3/16” tube soldered into the hole. The drill press was used to set it at right angles to the strip for soldering. The strip was joggled, to ensure the rotating paddles cleared the support beam, and with the 3/16” tube on the side nearest the hull. The brass strip was clamped to the support beam, with the complete assembly in place, and the pivot position adjusted to give the optimum motion of the mechanism. The brass strip was soldered to the support beam, and then removed and painted.
The paddles were cut from 0.050” styrene, the attachment points for the support arms drilled, and the support arms fitted and glued in with epoxy. The paddles and the side wheel assembly were painted black, with small pieces of masking tape over the pivot holes in the paddle support arms, where the pivot tubes were glued to them, and painted over later. When it came to assembling the parts, the sequence was as follows: - Fastened one end of the links to the inside face of the master rod (looks like a banjo); using #2-56 UNC bolts with the bolt heads on the outside face, a 4.5mm length of 1/8” brass tube as a bushing, and two #4 washers, and a #2-56 nyloc nut. - Inserted a #4-40 UNC bolt and washer in the centre of the master rod from the inside, secured it with a 5/32” brass tube bushing, lock washer and nut - Fastened the outer end of the links to the paddle arms, with the links on the outside of the paddle arms, with the bolt heads on the inside face, otherwise same as inner end of the links. The next step is to make the support for the pivot of the feathering mechanism.
The two side wheels are held together by 5/32” outside diameter brass spacer tubes. Seven tubes were cut to the same length, one for each paddle pivot location. There is an additional central tube of 7/32” OD to fit over the drive shaft. The assembly was placed on a drill press with a 7/32” size drill through the centre to align the two wheels, and hold them at right angles to the centre shaft/drill. The pair of side wheels were first soldered to three brass spacer tubes. A drill or a piece of steel rod was used as a mandrel to align them. Unfortunately I used the wrong flux and the rods and drill were soldered in, so had to be de-soldered. They were re-soldered using a different flux and aluminum tube to align the wheels. The remaining tubes were soldered in the same way. Some of the solder found its way into the clearance space inside the brass tubes, making the aluminum tubes a tight fit. After they were pulled out this solder was cleaned out with a reamer. Dave, Stephen says the only way (other than Youtube) to display a video was as I did.
The holes in etched parts are not always as accurate as drilled holes, so some holes had to be opened out with a reamer. The pivots for the moving links were to be held together with nuts and bolts, all in stainless steel. The bolts fit through a 4.5mm length of 1/8” brass tube which acts as a bushing. The links were bent slightly to ensure that the bolt heads and nuts cleared other parts. One side wheel was assembled with its associated links and set up temporarily, using styrene fixtures made to suit, to check that it operated as planned.
This model sails well but lists slightly to one side or the other when the paddle wheels start turning. I have been told this was not uncommon on full size paddlers, a phenomenon known as “digging in”. The only improvement I can think of for this is to fit feathering wheels. After waiting many months for the one remaining supplier who lists them to have them available for purchase, I concluded I'd have to make my own. So I prepared artwork for the parts using Inkscape, and had PPD in Scotland photo-etch the pieces in 0.9mm thick nickel silver. The only parts not included were the paddles which I planned to make from styrene to save some weight. (The big pointy part is for something else).
You might find this useful, although I haven't tried any of the methods: http://www.wikihow.com/Patina- Brass I've used the special patina fluid shown here: https://www.etsy.com/listing/9 298547/8-oz-black-patina-chang es-silver-solder Roy
How about a rectangular wire frame lying on the ramp with the RIB sitting on the frame. Attach the upper end of the frame to a short vertical arm of material, and have that sit in a narrow slot at the centre of the ramp. Open the door, have a servo push the arm with the frame and RIB down the sloping ramp and into the water. Retrieval would be the reverse. Painted a suitable colour the frame would be almost invisible. This assumes the gate will go low enough for the frame to clear it. Looks like it's going to be a great model.
That could well have been a solution. However, a trial I ran this morning has established the minimum axial length for the rudder. With a 40mm length and greater, straight line sailing was very good, with 35mm it now tends to wander away from a straight line. So one of my winter projects will be to make two new rudders 40mm long. Thanks to everyone who provided input into this quest. Roy
Hi Haverlock, In my original post I mentioned that I had tried a couple of different gyros and neither had made any noticeable improvement. The rudder movements were very small in off-water trials, presumably because helicopters are much more sensitive. I have increased the size of the rudders and that has made a big improvement. I am in the middle of tests where I am reducing their size step-by-step. I have not yet got down to a size where I get the original poor sailing. Roy
That's true, but I need much more capacity for powering the motors than for the lights. Another option is to put two batteries in parallel for the motors, with a third 6V battery in series for the lights. The batteries are already being charged individually. Interesting option. Roy
I'm happy to report that increasing the rudder area has made a significant improvement in this model. The as-built rudders on the model are ~8 sq.cm, and I have temporarily increased this to ~27 sq.cm., more than 3 times. The biggest dimensional change is in the fore-and-aft length, so they are as long as they can be without projecting beyond the stern of the hull. Today was not windless, but even with slight gusts of wind it sailed along serenely with barely a touch on the rudder to keep it straight. Also surprising is that it will no longer "turn on a tanner". Also , turns are much smoother and better controlled; can only be due to the rudder change. As on the last trial, it is sitting slightly lower in the water, but I think I'll leave it that way. The next step will be to reduce the length of the rudder in decrements of 5 sq.cm. and see what effect that has. Roy
I have seen reports that the units using oil (or "distillate") leaves deposits, although I have not experienced that problem. They also smell. Glycol is used in the fog units you see in theatrical shows, so I don't think they will leave a deposit. I have not experienced a stability problem. The SMU unit will hold about 350ml of water, but can only use about half of it (the top half :-). So the weight reduces but the centre of gravity also lowers.
The Steam Master Unit uses water which is vaporised by an ultrasonic nebuliser. It looks very effective and draws a reasonably low current. For both of my models, I built my own tank from styrene to suit the size and shape of my model. It comes supplied with 20mm dia discharge piping. One of my models had a 13mm dia funnel discharge. This cuts down on the flow (but still looks effective) but also requires a conical reducer from 20 to 13mm to make it work. Another model has the Harbor Models oil-filled smoke unit. It has a 1/2" discharge, a small tank, and draws 3A. I have not come across a unit which uses glycol, but would be interested to learn about one. Roy