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Model Boats Website Team
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Will send you the plans (such as they are - these are sections and the General arrangement) to your personal address. I am pleased with the model from ever perspective. She sails well and looks good; was also a rewarding challenge to build. She does require either skill or much patience to build.
Winter seems to encourage modeling, have spent many hours in hibernation working on the deck and superstructure details. A supplier offers a full set of Perkasa fittings, most of which would work on the Brave B. At one point considered buying a set. They are made in both resin and cast metal. Eventually parsimony prevailed, so only purchased a small number of hatch covers and other intricate shapes that would be difficult to make well. The items duly arrived and the quality is good. Was surprised by the weight though, so am pleased had embarked on making the other items from the usual materials. There should be an overall weight saving, along with a reduction in my surplus styrene and wood stock. One of the design tenants of the Brave class was flexibility. The vessel could operate as a MTB, MGB or Raider, or with a mixture of these capabilities. The weapon mountings were designed to allow armaments to be installed and moved around to suite the requirements of the role. Have reviewed many Brave class photographs trying to establish a “standard” armament configuration, to reproduce. Not only does the configuration define the weapons installed, it also establishes the ammunition and flare storage cabinet arrangements. Eventually decided upon the 2 x 40mm Bofors gun arrangement with 2 x 21” torpedoes and 4 x extended range fuel tanks. The model is now essentially complete. No doubt as I keep examining it will add further small details and refinements. Only disappointment so far is that it does not achieve the original weight target of 6 lbs, it is 9.5 lbs. The 6 lbs may possibly have achievable using one screw and motor etc., but once three are installed, not likely. The real test is when finally back on the water. Will close this blog then with a concluding report.
Unless you are determined to build to scale, the single motor/screw combination is probably the best. Have encountered several challenges with my triple motor/screw Brave Borderer (the predecessor to the Perkasa) layout. Now have the satisfaction though of setting off to build a scale model and have achieved it.
Well Canabus, certainly fast! Very envious of seeing open water too. If was not obsessed with building to scale, looks like your power train combination would be ideal. Once the water is Canada regains liquid form will be returning to my Brave B. Am confident it will now be much better, although potentially still overpowered. Have various methods available for controlling the performance in mind now. However, if nothing really works could, with some minor modifications fit a powertrain rather like yours. More food for though!
Thanks for your suggestions. Once we get back on the water in the Spring will investigate further. My last run in the fall indicated that the performance was now satisfactory and predictable. Cannot wait to try again and confirm. This is my first foray into a high speed vessel and it gives plenty of food for thought as even minor adjustments can make a big impact
After completing the cowl, turned to the rear structure covering the gas turbine and other engine spaces. This can readily be made from styrene sheet. The sides and top were cut out, reinforced with “L” shaped angle and fitted together with CA glue. No particular challenges, other than determining where the various section transitions occur. Luckily had two different sets of plans to compare, so the nuances could be established. It was not until the rear structure was fitted into the cowl, the assembly fitted to the removable deck and placed on the hull, realized just how important this milestone was. Once everything is firmly located the accuracy of build becomes readily apparent. Any inaccuracies show up as an obvious misalignment. Was able to check the alignments and squareness using eye, rules, squares and a spirit level and was pleased with the outcome. A subtle sanding of about .020” off the base of one side of the superstructure and everything became square, parallel and correctly aligned. Quite a relief! Have always stressed the importance of accuracy throughout a build. This supported that recommendation. Once the superstructure was completed realized my plan to lift the deck off to gain access to the electrical control switches was impractical. Have thus cut a small access hole in the rear deck to facilitate access. Still undecided how to best disguise the hole, but at least access is now relatively easy. From now on, until the test program can be continued on the water, will add detail to the model. Doubt there will be much to describe is that of interest, or that has not been covered by others. Will continue this blog once there is anything significant to report. In the meantime, best wishes for Christmas and 2019,
Hi Kevin, Yes I did, because of the complexity of the shape that was another technique that could have been used. I decided to use glass fibre as the cowl is around 7" wide and 3 1/2" deep. Considered a draw of that depth was beyond my skill and facilities with plastic sheet. If they are available it would have been a good approach. The more I work with glass fibre the more forgiving it seems to be. Not many mistakes that cannot be disguised or corrected! Rowen
Back to the build. Next milestone, to complete the superstructure and engine covers. The superstructure is essentially a cowl that supports the open bridge and serves as the air intake for the gas turbines. The engine covers fit into the rear of it. The superstructure is full of curves and will be interesting to make. Still trying to save weight, decided to make it out of glassfibre. Rather than first make a plug then a female mould and finally the cowl, wanted to try the technique of making a plug out of styrene foam sheet, then covering it in a glass fibre matt. Once the glass fibre is set, the foam is dissolved out using a solvent and the cowl remains – Inshallah! To ensure the foam did not react to the glass fibre resin, painted the finished cowl with enamel paint before sticking the matt down. See pictures. What a mess! The resin had crept under the paint and into the foam dissolving it. When the resin dried the plug had shrunk slightly and had the surface finish of a quarry. First thought was to hurl it and start again, this time in wood. On second thoughts, wondered if the plug could still be used. Decided to build it up with wood filler and from it make a female mould, as originally intended. The cowl would then be made from the mould. Built the damaged plug up and sanded it smooth. As the plug would be covered in fibreglass, the surface finish was not critical. Brushed a coat of fibreglass on the plug and, after drying filled any defects with glaze putty and sanded smooth. Once the finish and dimensions were satisfactory, applied a thicker coat of glass fibre to the plug. This was again smoothed down, waxed with carnauba polish and then covered in mould release. From it the cowl was made. Picture shows plug, mould and cowl placed side by each. The cowl requires reinforcement; the fittings and various mountings then adding before installing. A trial installation showed that it fitted properly the deck and was accurate. A lesson for the next time is to make the plug and mould much deeper than the finished item. That will allow any rough edges, on either the mould or the component, to be trimmed off leaving a smooth fibreglass edge.
Doug, Am using the HobbyKing 50A Boat ESC 4A UBEC along with their programming card. The diode explanation makes sense so will fit one. jbkiwi My battery -ESC and ESC -motor wires are short, probably around 4" each. The addition of capacitors as suggested is intriguing as have never heard of it before. Think it is easier to keep things together in a boat, whereas with an aircraft pitch trim becomes a factor. Am using 2S batteries with a 50A ESC, with the motor max current of 30 A. Have you any idea what size of capacitor I should use? The Tx/Rx combinations are almost infinite as the ESCs are programmable too. Just wish the ice would go so can experiment! Thanks both for your help, with this hobby you never stop learning.
Thanks jbkiwi and RN in Munich for your suggestions: Have never used Ali Express, those components look interesting. Will follow up. I have used a battery alarm of the type suggested and it does work well. Have a couple for use once back on water. The rule about adding a capacitor into the ESC circuit is new to me. Have ferrite rings fitted so will now explore adding capacitors too. Are these is series or parallel with the wiring? The relays are not used with diodes or any electronic gubbins. Wanted to make the circuit as simple as possible for a Mechanical Engineer, so used one separate relay per ESC. The relay operation is controlled by a RC switch off another Rx channel. It seems to work. Am aware of the back feed possibilities and hope to have avoided them with the separate circuits. Appreciate any thoughts though, can add diodes if necessary. Am using a new FLYSKY 10 Ch. Tx/Rx on this model which opens up a host of programming opportunities. Am experimenting with various features such an the interval between Fwd/Rv also limiting ESC response. As am now using the brushless motors essentially in unison, also toying with controlling the 2 x ESCs on a “Y” lead on a single control. Much to think about, pity our winter has arrived early and the pond has been converted to a skating rink.
Thanks Doug, always appreciate your thoughts. The relays are in a NO mode, so only operate when selected. On the bench works fine. Perhaps you do not have the same modulation issue as you are using 1000Kv and I am 2200. My motors respond rapidly, particularly around the fwd/rev position, so am always trying to accurately centre the lever. The motors I choose have integral cooling jackets and are nicely made. If they had been available in a lower rating would have probably used that. Good luck with the PT boat, looking forward to hearing what you decide with the powertrain. Good luck with the "C" check oug. Best wishes R
Finally the new brass propellers arrived, delayed about a month in one of Canada's regular postal disruptions. After minor modifications to the boss profile (the brass are more streamlined and thus longer than nylon) to give clearance with the rudder leading edges, they were easily installed. Could now refit the electrical equipment previously removed to get access to the shaft couplings. Inevitably took the opportunity to make “improvements”, so then could not get anything to work! After much frustration determined the problem was not from my improvements, but from the cheap and nasty slide switches provided with ESCs. These must have got damp during the test runs and corroded internally. Suggest when using these switches they be consigned to the garbage and replaced with proper toggle ones. Had decided to use the centre brushed motor/propeller for manoeuvring and low speed operation and then the outer brushless for high speed. Brushless ESCs do not modulate smoothly and motor operation is erratic. This was particularly evident when going from forward to reverse and vice versa. Using a lever control Tx, it was also easy to inadvertently operate the brushless control along with the brushed making the model response unpredictable. After some thinking, decided to insert a small relay into each of the white signal wires for the brushless motor ESCs. These relays would be controlled by a RC switch operated by another channel on the Rx. Hoping this way the brushless motors could be switched on and off whenever desired. The two relays would retain the ESCs as separate circuits and avoid any interference between them. The idea worked, can now operate the brushed motor confidently knowing the brushless will not be inadvertently triggered. This means low speed manoeuvers can be gently undertaken using the modulation and control ability of the brushless motors and, by selecting the auxiliary control, can add the high speed capability of the brushless. Am also hoping that when the Li-Pos trigger the low voltage cut-outs in the ESCs, this will retain a “get-home” facility on the brushed motor as that ESC operates independently. Much to look forward to when next on the water.
Used a small 6 - 12 volt pump bought from E Bay. Have used windscreen washer pumps before, but they are relatively heavy and bulky. This was quite compact and light and were closer to my weight restriction.
The pump was installed to give positive water flow even when stationary. Felt this would ensure cooling under most conditions. The plumbing is quite torturous and suspected there might be a significant head drop in the circuit. With the wisdom of hindsight, probably overkill; the water scoop between propellers may prove adequate.
Think a bilge keel should be the first step. My next suggestion would be to add some of the ballast to a removable fin keel, bolted to the underside of the hull. This will increase the righting moment, but not the weight. This can be seen if you examine U Tube videos of cruise ships and liners. They have so much superstructure they are inherently unstable. Have built several freighters and always fit captive nuts into the keel or underside. These are intended for trunnion display mounts, but have always been prepared to bolt a keel on if needed. The nuts can easily be sealed when sailing.