Topic: Newbie with questions (Read 6204 times)

28-12ARC · « **on:** March 22, 2015, 05:01:41 pm »

Hi Guys/Gals,
Hope everyone is well.

I'm a newbie to the forum and to model boats as well so please excuse if my questions appear a little daft.

I've been flying rc models for 10-15yrs and decided a change is needed. I've always fancied rc boats especially the ww2 era and even took the plunge a few yrs back and got a Robbe u-47 which is still boxed!!.

I've recently been reviewing the MTB 488 by Deans Marine, nice boat , good size(1/24) and will double as a nice static. This style and size ticks all the boxes for me but I'm a little unsure of certain aspects.

1. Power options - can I utilize the brushless/lipo/esc applications that I'm familiar with from aircraft.
2. Power to weight ratios- does the basic rule of flying apply to this sport ie:- 100w/lb for reasonable scale flying, are boats similar?
3. When you start drilling holes in the hull for prop shafts , rudder control etc how are these sealed from water coming in.
4. Balance /c of g - Are there basic rules or do's and don't that I need to apply when constructing the kit(s).

Sorry for the questions , I've a pretty good idea on most of the above but would rather not spend £300+ plus on my pride and joy and see it sink on its first outing so will take on board any advise or help given.

Many thanks

dougal99 · « **Reply #1 on:** March 22, 2015, 05:20:30 pm »

Welcome to the forum. You'll get plenty of advice here. some of it actually useful

With boats you're turning a smaller prop through water so I'm not sure aviation rules of thumb would apply. A/c ESC's don't have reverse, advisable on a boat. Holes can be sealed with car body filler or epoxy resin. When building you need to keep the superstructure as light as possible to stop the boat turning turtle. Trimming the boat to float correctly can be done with ballast and batteries.

HTH

Doug

Netleyned · « **Reply #2 on:** March 22, 2015, 05:21:29 pm »

Welcome to the mayhem

You can talk to Ron at Dean's who will put you in the picture as to power for the model you are interested.
They are not too far from west Midlands if you fancy
a road trip.

Ned

28-12ARC · « **Reply #3 on:** March 22, 2015, 05:31:12 pm »

Thanks guys for the info.

Sealing holes with filler/epoxy is guessed but how do you get a water tight seal ?
Good advise on the esc's I never thought of reverse.

I suppose thinking about , keeping the weight low in the hull will give the model a more stable poise in the water !!!
Its early days yet but already picking tips.

Thanks Fellas.

Andy

radiojoe · « **Reply #4 on:** March 22, 2015, 06:33:58 pm »

Hi Andy,
boats are not so exacting as aircraft you can use brushless and lipos but they work just as well on the cheaper brushed motors and nimh batteries, don't worry about the sealing of the shaft/hull, just keep the openings for the shafts as neat as possible and once the shafts are lined up and temporarily held in place seal the outside with masking tape or similar and apply a generous amount of epoxy to the inside around the shaft/hull, when set remove tape and tidy the outside with filler, it's as simple as that and it won't leak, seal the rudder tube the same way and make sure the tube is above the water line, all boats will need extra ballast to get them down to their water line once the build is finished especially the larger scales the ballast is also used to trim out any listing etc. If you have built and flown aircraft boats will be a doddle for you.

Arrow5 · « **Reply #5 on:** March 22, 2015, 07:34:15 pm »

..and of course the prop tube and rudder tube filled with Vaseline or similar light grease will stop most of the leaks.

tigertiger · « **Reply #6 on:** March 23, 2015, 01:03:55 am »

Quote from: arrow5 on March 22, 2015, 07:34:15 pm

..and of course the prop tube and rudder tube filled with Vaseline or similar light grease will stop most of the leaks.

Vaseline or white grease are better than the grey/black grease as you will always get some seeping into the hull. The black grease can leave an ugly dirty mess.

radiojoe · « **Reply #7 on:** March 23, 2015, 08:21:25 am »

I prefer to use the Raboesch Waterproof Propshafts a bit more expensive but if your spending £300 on a boat I think they are worth it, I've never had one leak yet.

sean Half-pint works · « **Reply #8 on:** March 23, 2015, 08:42:43 am »

LiPo batteries can be used, but as previously mentioned the NiHm type are cheaper and just as good. A good number.of people on here use SLA (Sealed Lead acid) batteries. Some time ago, a mentor of mine said "why add more ballast when another battery is more useful"

Balance wise, after Rc aircraft this will be a doddle, pop the hull in your test tank (bathtub when SWMBO is not looking) and aim to get the painted water line level with the water.as with aircraft try and keep the weight even between port and starboard. Also keeping the C of G is generally a very good idea for most boats, again common sense applies.

Welcome.to the forum and have fun

Sean I

28-12ARC · « **Reply #9 on:** March 23, 2015, 10:10:17 am »

Hi Guys,

An abundance of help and ideas.......................I'm overwhelmed , thank you all.

One thing I've not mentioned is the kit I'm aiming for , Is the deans marine a good choice ?

Thanks
Andy

dougal99 · « **Reply #10 on:** March 23, 2015, 11:09:42 am »

Like everything else opinions vary. However, there are a large number of modelers who have built lovely models from his kits and some have won significant prizes. Why not visit Ron and see the completed boat in his showroom? You never know you might even get a coffee!

Perkasaman2 · « **Reply #11 on:** March 23, 2015, 11:54:35 am »

Hi.You can have a single or double propellor setup. Brushless is certainly the best power option as motor is smaller and lighter and gives a lot more power. I recollect that this is quite a heavy model when completed and weight saving lipos must be an advantage because of their superior power/weight ratio and the model will actually plane at speed.The deans is an ideal, good looking starter for your interest in WW2 Coastal Craft. I would not consider the brushed motor/s.l.a. battery option to drive a hull of this size. Single rudder/prop is much simpler and easier to install although a full twin setup is possible and twin esc's enable independant control of props to enable twin stick/tank steering. The original boats were triple engine/prop but this installation entails considerable planning and thought to pull off successfully. The KISS principle - keep it simple and straightforward is always a safe option. Authenticity both above and below the water line is more difficult and problematic.
Performance is important as is endurance, ideally you want to have both. You don't want to end up with a 10 minute sail at the pond. You have lots of choices.

28-12ARC · « **Reply #12 on:** March 23, 2015, 06:10:46 pm »

Hi ,

With not having the kit yet there's a lot of guessing I'm doing but I'm going to try and utilize my brushless set ups and esc's . Although not with reverse capability the esc's will get me going initially.
I'm aiming for two brushless motors giving around 400w each with a current draw of around 30amps each. Two esc's rated at 40amps each and a 4s 5amp lipo should ensure that power is plenty whilst all components are well under there operating limits. The kit will be coming in at 6-7lb so this set up should be more than powerful. With no airflow or cooling over the components I'm hoping to "over enginner" things so they are not stressed or no where near there limits and hopefully stay relatively cool.

The only unknown quantity is the two props. Two blade, 3 or 4 blade, brass or plastic and pitch ???

decisions, decisions !!!!

Andy

radiojoe · « **Reply #13 on:** March 23, 2015, 07:05:53 pm »

Kits usually include recommended components for running gear and Deans certainly do, size and type of props/motors etc.

Perkasaman2 · « **Reply #14 on:** March 23, 2015, 09:00:52 pm »

Hi Andy. Its important to install your propshafts as horizontal as possible to give the most efficient thrust angle and this is enabled by bolting/mounting the motors as close to the hull bottom as is possible and using longer shafts. Your batteries placement will be between a third and halfway measured from the bow. In other words just forward of the mid point of the hull. Too much weight further back will cause snow ploughing and may bury the stern. I have used velcro strip and blue tack in the past to allow options in positioning batteries during running trials.
A really useful reference book is 'Allied Coastal Forces of WW II' - Volume II by John Lambert & Al Ross. This book is a mine of useful info and pics.

28-12ARC · « **Reply #15 on:** March 23, 2015, 09:20:23 pm »

Hi perkasaman,

Excellent info .............

I've noted the book ref and are searching. Already got one being delivered tomorrow -"Vosper Motor Torpedo Boats: From 68ft PV Boat to MTB 538 Specialist Hobby Book"

Andy

Perkasaman2 · « **Reply #16 on:** March 23, 2015, 09:57:08 pm »

Hi Andy. I was never concerned with scale accuracy below the water line and chose to maximise efficiency and performance. I chose to use black plastic 2 blade props as they are light and efficient and come in two versions 'S' or 'X'. The X is courser pitch and gives more thrust than the 'S' or Standard version. They are very inexpensive and you can easily source a range of sizes for running trials and temperature checks of motors. My guesstimate for a twin prop installation for the Vosper is 35S and I would certainly also try a pair of 35X for devilment. These would be my choices to try out using brushed motors. I have no experience of brushless and cannot therefore give a definitive opinion. Given the performance of a low kv brushless the Vosper should easily plane without full revs on 35mm props.
Indeed twin 30X may give adequate planing and much better endurance.It will be interesting to hear from Deans re a twin brushless/prop setup.

canabus · « **Reply #17 on:** March 24, 2015, 10:27:25 am »

I get my test plastic props from Hobbyking, very good price, so you can get a large range for testing!!!

28-12ARC · « **Reply #18 on:** March 24, 2015, 02:09:58 pm »

How does everyone test and trim there craft out. In the bath, paddling pools or local ponds. ?
What's the general opinion on rescuing a stranded boat. A 2nd boat or some sort of fishing line with a tennis ball attached.
I live at the back of a nature reserve with several deep ponds. Very nice, quite and some are secluded but access is difficult in some areas due to reeds.

Thanks
Andy

dougal99 · « **Reply #19 on:** March 24, 2015, 05:10:03 pm »

Where space permits I use the domestic test tank (aka Bath) for ballasting. Failing that a shallow, sheltered pond/paddling pool.

For rescue a second boat, preferably a utility vessel such as a tug with suitable fendering, is good as it can be used at a distance. A fishing pole/tennis ball combination is good for close work. As for reeds: you can end up with multiple boats stuck quite easily. If not too deep waders are a good idea, failing that an inflatable dinghy or somesuch is recommended.

malcolmfrary · « **Reply #20 on:** March 25, 2015, 07:39:34 am »

Quote from: 28-12ARC on March 24, 2015, 02:09:58 pm

How does everyone test and trim there craft out. In the bath, paddling pools or local ponds. ?
What's the general opinion on rescuing a stranded boat. A 2nd boat or some sort of fishing line with a tennis ball attached.
I live at the back of a nature reserve with several deep ponds. Very nice, quite and some are secluded but access is difficult in some areas due to reeds.

Thanks
Andy

For rescue, a tug or similar with a line attached. The script is to pass by the cripple, pass behind it, trailing the line, stop, and wind in by hand. But keep away from reed beds, rescue from there is likely to be a manned boat job.

Perkasaman2 · « **Reply #21 on:** March 25, 2015, 01:03:08 pm »

Hi Andy. Electric power is quite reliable. The usual problem when running fast trials may be rudder damage caused by floating or slightly submerged debris, however your twin prop tank steering should give directional control to recover. The second usual problem is losing props which have'nt been adequately tightened against their locknuts. This situation causes a real problem on a single prop installation as you can imagine. Even the lightest breeze will eventually bring a model to the bankside somewhere given time, although I do understand that this is the least desirable situation in your circumstances. I have always found the setup and trialling of a model very enjoyable. A careful approach is the key ingredient.

28-12ARC · « **Reply #22 on:** April 01, 2015, 01:48:34 pm »

Hi Guys,

Kits ordered and on its way. I've been advised to drop the cast props in the kit and get some nice brass replacements. From previous posts I think 35mm is the way to go with a left and right one in a 3 blade. Does anyone know if the fitting should be 3 or 4mm or is it wise to drop the shafts as well and fit aftermarket jobbies?
I'm looking to fit out two brushless motors with 4mm shafts so any help or advise on couplers , shafts & props would be greatly appreciated.

Thanks
Andy

28-12ARC · « **Reply #23 on:** April 05, 2015, 09:01:37 pm »

Had a good look at the kit today and very impressed. The hull is crisp and clean with no damage and not too much to trim. Deck fittings look very good and well made.

28-12ARC · « **Reply #24 on:** April 20, 2015, 10:30:52 pm »

Decided to drop the cast rudder items and go for some brass after market jobs with an 8mm threaded plastic tube and sealing washer.
Epoxied in and sealed. The kit versions were either very close or under the water line so not taking chances.
Swapped the props and shafts for some Raboesch brass replacements.
Tubes are lined up and epoxied into hull and onto the support frames. Just got to fill with p38 and sand n smooth.

Have fitted a standard size digital servo(Newpower) in the stern for the rudder . High torque and heavy which I think will help with ballast.
I'm guessing to test the hull for leaks prior to fitting the deck. I've noticed on this and other kits that once completed there's no access in the rear of the deck to get at the servo or rudder linkages. ???

Thanks
Andy

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Author Topic: Newbie with questions (Read 6204 times)