View Full Version : Fresh water Central Scotland

1-Jun-09, 01:48 PM
After some length of time, I have at last got the craft running, although it still looks a bit rough. I have tested it out on a field, but really want to get it on to water. I think that I would get jailed if I took it to Loch Lubnaig, so thinking about Loch Earn, Loch Lomond or Loch Tay. I have an offer from a friend who has given me permission to try it out from his land onto Loch Voil. So any ideas would be helpful.

Jon Pert
1-Jun-09, 02:19 PM
From memory you have a 503 racing craft?

Apart from the noise issue and hacking off the locals you may have to think about the following.

Does the craft have plenty of buoyancy?
Will you have support to help you if the engine stops on water and you can't get it going?
How populated is the area you want to try it out in?
How open to the public is the area you are intending to use?
Do you have insurance for operating the craft?

If it is a racing craft a private lake would be a better option tbh. Noise is our main enemy (that and ebay specials causing havoc on beaches) so I would urge you to not operate where you are likely to cause complaints as it could cause problems if quieter cruising craft want to use the area in the future. :(

If the craft does not have enough buoyancy then it will sink. :eek: If it is a racing craft you cannot be sure that the buoyancy is still good or indeed still there from when it was made. Try a float test close to shore. Sit in it with the engine off for at least 10 minutes.

Just a few thoughts and of course if my memory is that poor and you do not have a racing craft then please ignore the above and we'll start again. :)

No doubt the Scots will be along shortly to add their 2 penneth!

Ian Brooks
1-Jun-09, 07:51 PM

What sort of craft is it?

Before you go out you need to think about these ...


Does it have enough freeboard? Does it have buoyancy?

Will the craft get you back? Can you get the craft back?

Have you got the proper gear?


If this is a race craft don't take it onto public waters, it almost certainly far too noisy, and will result in yet another hovercraft ban..


Is there independent means of rescue? Can you call for help?

Code of Conduct:

This is our Code of Conduct... designed to keep the peace with other water users!



Keith Oakley
1-Jun-09, 07:54 PM
Ah - familiar names of hover cruise sites in days gone by. I had a great week cruising around Loch Tay with Anita in '73 and remember well the 20+ craft club cruising weeks to Loch Lubnaig in '77 & '78. I remember with affection Jim Lynes campfire reflections on being recovered from the river below Strathyre's sewage outfall. And bombing down the measured mile on Loch Lubnaig in Spirit of Snodland at an awesome 38mph, as measured by the same guys who measured Campbells Bluebird a few years earlier.

But those were the days when the local Trossachs tourist board, anxious to increase visitors, would welcome you with open arms, and indeed invited you to come.

I have no idea what the attitude is in these 'ealth and safety conscious days, but as Jon says the quieter the better.

1-Jun-09, 09:09 PM
Hi Millar,

Where are you located? And - what type of craft do your have?

There aren;t many fresh water locations publicly available that I know of - plenty salt water areas though :)

2-Jun-09, 09:15 AM
Thanks for the advice.
Firstly, I remember the times well, when you all came to Loch Lubnaig, as Strathyre was home at that time.
I am going to talk with some members of the National Park, I know some of the board members personally. Yes, there are all sorts of restrictions, although if you can find where they written down, then you are doing better than me. Loch Lomond does have a registration scheme for all powered water craft, from jet skis to power boats, also the sea planes work from here. So could try there. Loch Earn also has water sports, jet skis, water skiing, sea planes land there and a couple of weeks ago, there were flying model sea planes around the place. Loch Tay also allows power boats, jet skis, the sea plane and water skiing, even the fishermen put up with this up there, we also have a fishing boat up there. Loch Voil has the sea plane landing up there as well and I have permission from a riparian owner, so could try there and its in the middle of nowhere. So, if you see that I am taking a lot of things into consideration. However if I still lived in Strathyre, then I wouldn't give a damn, local rule and all that and to hell with all the political bullshit.
So to the craft, yes its a 503, running twin 36mm mikunis and with a Rotax exhaust. I recon more noise comes off the fan than the engine. Its an old Vortex craft, built orginal by Ewan and wrecked by someone else. It floats.
I live in Callander, about 15miles north west of Stirling.

Keith Oakley
2-Jun-09, 11:05 AM
Given the amount of power activity I think you're in with a good chance especially if you talk to National Park board members. Most 503 craft I've noise tested, if they have a good exhaust, make most of their noise from the engine air intake and the fan. The fix is an airbox silencer on the air intake.

John Robertson
2-Jun-09, 12:22 PM
I have two craft registered on Loch Lomond and have used it several times in the past launching from Balloch or Milarrochay Bay. I've not used it since they introduced extensive speed restrictions a couple of years ago which make hovercraft operation almost impossible - you need to travel nearly a mile from the Balloch launch site to get out of the 6mph speed zone :(

The other Lochs are a bit too small for us nowadays :)

We may be on the Tay this Saturday afternoon if we can find a suitable launch site near Perth.

2-Jun-09, 01:26 PM
I'm going to be using the 503 for thrust on the Surveyor, what kind of intake or what would a intake silencer look like and be made of for the 503. :confused:

Jon Pert
2-Jun-09, 01:34 PM
Intake silencer for twin carb.


Intake silencer for single carb.


2-Jun-09, 04:28 PM
Ah don,t want to sound to negitive.... i have seen a 447 on a sev before!!! although the craft was good the motor made it top heavy,hard to protect from the elements and was very keen on sucking salt water down its throat. All the sev,s that work very well over here have been built to the plans the ones that have been altered............ Do not. Again the last thing i would want to do is run down your build and we wish you all the best of luck.

3-Jun-09, 10:27 AM
I have been pondering that, maybe getting a 4 stroke for the thrust as well. But who would want my Rotax ? not sure anyone would want it around here.

GARRY: Will call him now.

3-Jun-09, 11:34 AM
Thanks for your advice, I think if I get hassle about noise then the inlet silencer seems to be the way to go.
Basically I just want to have a laugh with the craft, nothing serious.
I think the west end of Loch Tay and Loch Lomond would be the way to go. Millarochy Bay would be almost ideal as you don't have to go too far before you can exceed the 6mph speed limit. The west end of Loch Tay has some good launch points and I think I can use the slip in the village, then go down the Lochy out to the Loch.
So when I get things sorted where I can use it without upsetting locals, conservationists, do gooders, etc I will let you know.

3-Jun-09, 04:15 PM
please dont mess things up for the rest of us, dont get me wrong we all are out for a bit of fun. but please invest in the silencer, it is not only the cost of the parts... its the cost to hovercrafting if you upset the public.

3-Jun-09, 06:04 PM
Jon is that air intake silencer the sort of thing members are fitting to reduce noise?

I would have thought the air filter element would have to be inside the box with a air duct feeding it to really bring the noise down or am i missing something
Filters in open air are noisy and clog up with water and dust really quick
not good for a hovercraft in my opinion.

Jon Pert
3-Jun-09, 06:38 PM
We did some tests on it with Keiths noise cam and it did bring the noise down I believe, I forget by how much I'm sure Keith could let us know.

I ran a 447 on the Severn with an intake silencer and the filter didn't cause a problem (the bendy fuel pipe did though!) in the 3 or 4 hours it was out there.

An intake silencer and after muffler do help, as much as is possible with a 2-stroke. A well designed engine cover will also help to keep noise down and spray out, not so easy when the fan is driven off the gearbox though!

3-Jun-09, 08:26 PM
The thing is you don`t need to bolt the air filter to the engine,it could be fitted lower down in the hover in a cleaner air position and linked to the engine air intake with ducting.
There are loads of after market parts available out there , a lot of them are not designed for our type of environment
In the real world machines designed to work in dusty or wet environments have good quality filters fitted to prevent down time on the job, I don't think hovercraft's are any different


Keith Oakley
3-Jun-09, 08:28 PM
From memory it dropped the intake noise significantly but the overall noise only came down a couple of dba (which isn't very significant) because of the fan noise - caused largely by turbulence from obstructions (frames, belts, splitters etc) being too close (within 100mm) of the fan. I was impressed by the low noise from a 50-60bhp rotax 2 stroke in a hovpod recently, due to the excellent air intake box and after muffler. The craft wasn't quiet overall because of fan noise probs but thats another story. It does show that a 2 stroke can be much quieter although I think its still beaten by a low revving (<4500rpm) 4 stroke.

The airbox is essientially a helmholtz resonator tuned to the engine firing frequency. In electrical terms the box acts as a capacitor supplying air quickly to the engine as it sucks air in on each cycle, whilst the intake to the airbox is a restricted size acting as a resistor to slow the refilling of the capacitor. This tuned circuit means that the pressure fluctuations (ie acoustic noise) reaching the outside world are smoothed (thus quieter). It does mean any old box won't do, it must be designed to fit that engine.

I would have thought an exposed mesh air filter wasn't a good idea, particularly with salt spray.


4-Jun-09, 05:41 AM
OK, so what you saying is:

If I buy one of these air boxes, and a after muffler and then enclose the motor like I was going to anyway, and being that is is going on a Sev.

This should be enough to keep the green peace guys happy.? Right ?

Keith Oakley
4-Jun-09, 09:00 AM
...and keep any obstructions away from the prop. That'll make that particular design as quiet as you can, and thus more acceptable. But noise acceptance is subjective and without a stated dba limit and objective dba testing to prove you meet that limit you can't say it will be acceptable to everyone. but hey go for it!
Bye the way my tests show relatively little noise comes from the engine body (except in cases where the engine is about to seize) so enclose it for reliability reasons ok but don't forget its an air cooled engine and could overheat, especially in Africa!

4-Jun-09, 12:47 PM
Yes I have solution to that, a gauze hole in front of the engine cover to let air flow through. If I can I also want to mount the motor just above the lift engine so that it gets as much air as possible but as low as I can for better wight distribution. The last thing I want is a top heavy craft that falls over every time I turn. With the fuel tanks placed on the floor on either end it should keep the craft well balanced.