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Author Topic: multi boat silak  (Read 6208 times)

wicked999

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multi boat silak
« on: March 15, 2009, 07:01:17 PM »

hi there I'm after some help on my multi boat silak took it down the lake to day went well but when i opened it up flat out the back end was all over the shop would not go in a straight line
i hope someone can help?
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john54

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Re: multi boat silak
« Reply #1 on: March 15, 2009, 08:11:18 PM »

Rudder flexing , play in links ,servo weak or loose {:-{ someone on here WILL have the answer :-))
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andyn

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Re: multi boat silak
« Reply #2 on: March 15, 2009, 10:46:53 PM »

Post photo's :-))

We can see what we can do from there O0
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wicked999

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Re: multi boat silak
« Reply #3 on: March 17, 2009, 09:35:12 AM »

this is the boat
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wicked999

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Re: multi boat silak
« Reply #4 on: March 17, 2009, 09:38:14 AM »

and
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wicked999

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Re: multi boat silak
« Reply #5 on: March 17, 2009, 09:41:21 AM »

on the boat now is a diffrent tuned pipe and a tn2 carb prop is a 2026
thanks
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john54

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Re: multi boat silak
« Reply #6 on: March 17, 2009, 03:42:45 PM »

Iam no expert  :(( But the rudder looks a tad on the small side.
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andyn

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Re: multi boat silak
« Reply #7 on: March 17, 2009, 04:38:00 PM »

The rudder is fine, at the speeds multi's travel at you'd be surprised how little they need to turn. For example a line of eyeliner down the bottom of the hull if carefully placed will actually stop any leaning  and improve handling characteristics.

Try holding the rudder in one hand and moving the control stick on the radio, this will show you if there is any slop in the connection. There should be a good deal of force pushing against your hand with a fully charged reciever battery. If servo turns and rudder doesn't, theres definately something wrong.

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andrewh

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Re: multi boat silak
« Reply #8 on: March 17, 2009, 04:58:07 PM »

Andy,
interesting - the eye liner :}
Does this explain why your eyes also looked a little uneven at LLLLanberis

Wicked
I make no claim to specific knowledge but it looks to me like a system with very little "skeg" in the water at speed.  She must rise so that only the stern few inches (if that) are in the water - the prop is thrashing in an air/water mix of variable density, so the torque and steering effect is quite variable
There is only the rudder  and a little of the prop shaft support to provide linear stability - if she was mine I would try a shallow skeg maybe 1/4 sqare balsa aft of the rudder, or a little shark-like fin ahead of the prop (hard alloy or CF sheet bonded onto the side of the propshaft)
I have been wrong before, but these would test my supposition
andrew

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andyn

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Re: multi boat silak
« Reply #9 on: March 17, 2009, 06:07:08 PM »

The best thing to try if it isn't the rudder is some turnfins on the back of the boat.

Everything about a multi is designed to be as drag free as possible, so adding bits on isn't really an option if you want to go fast. Multi's are thus like little missiles, so the crashes are spectacular...

Search youtube for FSR-V for more videos, a selection for you here...

http://www.youtube.com/watch?v=eCb9hVAnH_o&feature=related

http://www.youtube.com/watch?v=wFfdsYz5q2w
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SteamboatPhil

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Re: multi boat silak
« Reply #10 on: March 17, 2009, 09:05:19 PM »

I was quite amazed how small the rudders were on the boats I saw at Hove at the weekend, small rudders and a turn fin certainly do work.  :-))
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omra85

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Re: multi boat silak
« Reply #11 on: March 17, 2009, 11:16:05 PM »

The Silak was designed many years ago by a World Champion George Merlotti.  It was (and maybe still is) used by some of the Coventry multi racers with great success.
One of the most notable things about its design was the very small rudder which, at racing speeds, turned the boat very quickly.
Most multi boats have quite small rudders as the larger the rudder, the more the drag.  The only downside is that the boat does not turn well at low speeds - but who wants to go at low speeds anyway?
The straight line instability is usually down to one of three factors -
1. if the shaft angle is too steep, the extra lift generated will make the boat "flip-flop" from side to side (yours looks fine in this respect)
2. if the shaft end has not got sufficient support causing it to oscillate (again, yours looks well supported)
3. or the most likely, play in your rudder control.  I notice that you use a separate radio box. Is this well fastened into the hull? Is the control rod strong enough? Is the servo firmly mounted in the box? As Andy said, if you turn the radio on and leave the stick central, there should be NO play on the blade and it should take a deal of force to move it (don't try too hard or you'll strip your servo gears).
When you move the stick fully over, the blade should remain in that position without being able to travel further.
Finally, do a range check with someone watching the boat. The rudder should follow your commands without any 'twitching'. (This MAY only happen with the engine running as it is often caused by metal to metal vibration contact).

If NONE of this helps - save up for a 2.4GHz radio  O0

Danny
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Bill D203

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Re: multi boat silak
« Reply #12 on: March 18, 2009, 08:12:30 AM »

Hi Danny
Looking good from down under. See when I get back.
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wicked999

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Re: multi boat silak
« Reply #13 on: March 18, 2009, 09:25:25 AM »

i have got a 2.4Ghz radio system :-)) i will look into the radio linkage thank you for your help . any more suggestions would be great and any tips to get more speed
thanks Matt
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omra85

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Re: multi boat silak
« Reply #14 on: March 18, 2009, 01:29:21 PM »

Hi Matt
What engine are you using? Looks a bit like an SC 61 - if it is, then you're going to have to spend some time on it to get near the power output of a 'standard' rear induction, front exhuast motor. The sports engines are fairly low revving so you will need a long pipe length, probably around 32-34cms from plug to cone (following the bends in your manifold).  You said you have replaced the carb with a TN2, what bore is it?  For flat out speed you will need at least a 9mm bore - maybe more if you don't lose your throttling.  Are you intending to race it or is this just for fun (not that racing isn't fun ...).  Finally what pipe have you changed to? If its a Prestwich then it will have the starting length for a 10cc provided.

Hope that helps

Now a message for Bill - (as he's not used to the language "down under" yet)

Danny  %%
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wicked999

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Re: multi boat silak
« Reply #15 on: March 18, 2009, 04:38:01 PM »

hi the engine is an asp with tn2 carb 9mm . is that the wright pipe measurement 32mm? someone told me around the 30mm mark was the best with the engine the pipe is a Genesis pipe from just engines 
im a little new to this how fast should this boat go?
thanks matt
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omra85

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Re: multi boat silak
« Reply #16 on: March 18, 2009, 05:22:26 PM »

Hi Matt
I've 'borrowed' this from Dave Marles Free Technical help page -
http://www.prestwich.ndirect.co.uk/techbase.htm
(there is also lots more stuff for beginner and advanced alike)

"Within a certain range you are able to decide what prop was the best for what pipe length and you are then able to set up your boat to run with this prop. Advanced mods are available but this however would require that you start working with the motor timing and does get a little technical. As a general rule the higher you make the exhaust port the higher your revs can go the smaller the prop and the shorter the pipe and vise versa, the lower you make the exhaust port the lower your revs will be the bigger the prop can go and the longer the pipe should be. This is all to a certain limit of course".

Therefore it is always easier to start long and then 'bring the pipe in' until you are happy. My suggested 32cm was erring on the side of caution as the engine is not designed for high revs and the 2026 is a reasonable sized prop for a 10cc.
Also, I believe, the Genisis pipe is a 'flat plate' type of reflector instead of the more usual 'inverse cone'. This means that the exhaust pulse reflections are very sudden, making the optimum distance very critical. You will probably notice a sudden 'drop off' in performance as you reduce the throttle - this is when the engine has'come off the pipe'. When you open the throttle there will be a surge of power at a certain point, which is why they are seldom used in racing.

As to the speed, I have no idea!!  You can use a GPS system for measuring straight line speed, or even timing round a carefully measured course.  I've always used the old method - if my boat can get past the ones I'm trying to overtake, all is well. If I can't get past, it's too slow!  :-))
(I've heard people quoting about 33mph for a racing 3.5cc, up to 60mph for a 35cc - if you can get 25 - 30mph you're doing well).
Danny
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andyn

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Re: multi boat silak
« Reply #17 on: March 18, 2009, 05:27:05 PM »

It'll be good to start with, and get your reactions up to that of driving a fast boat, but it won't be that quick. Genensis pipes are designed for throttling in aerobatic planes, so it'll be great in the corners, but without a 'screamey' engine, it won't be that fast.

Agree with everything Danny said there, was doing other stuff and typing at the same time, so he beat me to it

Still get used to it and I'll give you the contact for a guy who will sell you an engine setup.
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wicked999

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Re: multi boat silak
« Reply #18 on: March 19, 2009, 09:12:39 AM »

thanks andy and danny for your help it is somthing i want to get into. i would love to buy another boat and race omra so if you know any body selling any omra boats i would like to start racing. what is the best class to race in
thanks matt ;)
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andyn

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Re: multi boat silak
« Reply #19 on: March 19, 2009, 03:35:42 PM »

what is the best class to race in

I'm not starting an argument ;)

I think probably Z or AA class would be best to start with, they're the smallest and slowest of the lot, so would help you with driving skills and race tactics to start with.
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wicked999

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Re: multi boat silak
« Reply #20 on: March 19, 2009, 04:17:17 PM »

i would like to start with a larger boat  i which could have a 45 or 61 size engine is there any second hand hulls out there?
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john54

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Re: multi boat silak
« Reply #21 on: March 19, 2009, 05:26:29 PM »

You could try E*ay always something on there of interest :-)) BUT BE VERY CAREFUL  ok2 theres some right heaps of c*ap as well as some very nice sometimes over priced good boats :-)) If you do find something you like ask on here for advice as the gents on here will not pull any punches :-))
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andyn

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Re: multi boat silak
« Reply #22 on: March 19, 2009, 08:13:08 PM »

http://www.omra-uk.org/salesandwants.html

See the giant orange Magnum, 3rd one down. If I were you, I'd go for it :-))

Needs work doing to it but it'll take anything from a 61 nitro up to a 26cc petrol. Many people have them, mouded by Bernard Holder. Even or good friend Danny here has one O0
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omra85

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Re: multi boat silak
« Reply #23 on: March 19, 2009, 08:15:51 PM »

Andy posted while I was typing - I'm not sure it's still available but the Magnum would be a very good starter (providing you can lift it)  :-))

Some good advice here already Matt.
Like Andy, I don't want to start an argument either  %)
Every different type of boat or size of engine has it's fans.  
Have a look at the latest OMRA results to see what racers are using -
http://www.omra-uk.org/resultsaadhove.html

The main thngs you need when starting out is -

something straightforward to set up (the more adjustments you have, the harder it is to get right).
something predictable (in racing, you need to know exactly what the boat is going to do in any given circumstance)
something easy to maintain (fibreglass [GRP] is cheaper and easier than kevlar, wood is lighter but not as strong as GRP)
something cheap(ish) (you want quality over quantity - a cheap reliable engine is a better start than a tuned racer)

With that in mind, I would suggest an 'A' class, up to 7.5cc (.46cu in) in a fairly robust hull such as a Crusader, submerged drive - which will give you slightly less speed but more precise handling, and a solid shaft, 2 channel radio for now (you may want to upgrade to a remote mixture control later on).  
The engine can be anything, but CMB are the strongest (also the most expensive). Picco, OPS, Rossi, OS are next in line then SC, MDS, Irvine, Just Engines, etc are the slowest and cheapest.

IF you can get a GOOD secondhand one, then great, you can save money and work. Unfortunately, they rarely come up and, as has been pointed out, there is a LOT of rubbish out there - especially on fleabay, and the LAST thing you need is to try and sort out someone else's basic building mistakes when you should be racing.  It will benefit you more in the long run if you put your own boat together as you will know how everything fits (or even why it has come loose!).

The OMRA site (link earlier) has a list of suppliers on the "Links" page as does the main Mayhem site.  You could always try a "Wanted" advert on either of the sites. To give you a vague budget figure, a good A class racing boat, well put together and with average use should be around 250 to 300 (without radio). That will include hull, fittings, tank, engine and pipe.

Good luck
Danny


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Bill D203

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Re: multi boat silak
« Reply #24 on: March 20, 2009, 07:31:48 AM »

i would like to start with a larger boat  i which could have a 45 or 61 size engine is there any second hand hulls out there?
Hi de hi from down under. "No Im not upside down just yet Danny". Glad to here all went well at Hove.
I have a Endforcer boat hull with fuel tank ,rudders, poss radio box for sale when i got back home. If you want it for a small amount It's yours. You will need to find a 26cc Zenoha + drive system and radio. This boat came 3rd at Windermere in 2007. Needs a little bit of fitting out work. Gose very well when last run. Email me direct .
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