Model Boat Mayhem

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 71 
 on: Yesterday at 01:41:23 PM 
Started by GrahamD - Last Post by clockworks
Thanks for the link to the Bruder figures - I've ordered a couple.


Also good to know that I'm not the only one who finds the "stance" to be a little nose down at rest - it means I didn't build it wrong!


I agree that running through other boats' wakes can be fun - as long as you aren't doing a fast turn at the time. This is the fastest boat that I've built so far, and it tends to skip a lot more than my slower boats.

 72 
 on: Yesterday at 01:14:03 PM 
Started by KBIO - Last Post by KBIO

First of all, what is the purpose of engine lubrication?
By definition, lubrication is intended to reduce friction and wear between two parts in contact and in motion relatively to each other. Considering the power of our engines, we understand that it is rather the friction reduction that we are interested in.We Steamer, then , have a problem to solve : we need to oil,  moving parts in a hot and dry environment! Every one knows that saturated steam is dry. Fortunately , if I dare to say so, the steam in our lines engines , if not overheated, will condensate a bit. We shall take advantage of it to make our oilers work.. This is this small amont of water which spread the oil all over the moving parts. The steam condensating when hitting the oil surface in the oiler.Now, we have to send oil in a water wet environment! Oil and water do not mix naturally. Not enough water and the oil stays in . Too much water and it makes nasty mayonnaise. What is mayonnaise then !It is an emulsion. In our engines, the steam is dry = basically no water- and mayonnaise cannot , a priori, forms. Unless the steam condenses a bit and , that little bit of water with oil will create an emulsion that will cling to the moving parts. The sliding valves are excellent beaters to make this mayonnaise! Let's take advantage of it !The mayonnaise hangs well on the walls The goal is is to obtain a good ratio. and as the best being the enemy of the good, we must allow the smallest possible volume of oil in. I always take the exemple of of a drop of oil on a wet floor to make the people understand that the combination of oil & H2O is what reduces the friction between the sole shoe and the ground. Some remember it by (painfull) experience.
But let’s keep it simple  .
Let's find a solution!
To lubricate our engines we need to find an oil which have the following properties:-It must have a viscosity that allows it not to disperse: viscosity is rather a state; when it increases, it opposes a resistance to flow. The state of a viscous fluid will flow without turbulence.-It must be fluid enough to allow it to flow out without doing it all at once. The more sleek a fluid is, the less it will resist to flow-It must be smooth, i.e. “weting” the surface to be lubricated. So spreading out well on the surface without discontinuation.-Must attach to the moving parts. Can not evacuate under mechanical (centrifugal) or thermal (steam) action-It must keep all these properties at the required working temperature.And now you have set a foot in: Tribology!
Tribology being the study of friction and the means to reduce friction.
T
oo complicated for me, I leave it to competent engineers!


There are several kinds of oils: animal, vegetable, mineral... we will talk about the one that best suits our problem.
Some use olive oil! Castor oil is however better lubricating.The viscosity of vegetable oils varies little with temperature, and these oils are particularly suitable for fixed-aperture lubricators, the flow remaining substantially constant. They are the most stable up to a certain temperature.....and stink ! I' have heard so much miraculous recipes on this matter!But at high temperatures, vegetable oils decays, acidifies and carbonises itself . We are talking here about temperature at 350°C (Tassignon.be)


The problem with olive oil is that if it fairly resists to temperature , but is not tha best oil for lubricating , and , it will eventually rub out the metal on a long run.
At the end, the most elaborated product adapted to our engines is mineral oil.
It meets all the conditions required to improve the performance of our engines under steam conditions.
The viscosity of an oil is its ability to not shear the oily film that separates moving parts under unconventional conditions.
An engine oil is proposed with different grades according to the needs and there is necessarily one adapted to our needs.
There are several units of measure of viscosity depending on whether it is dynamic or kinematic: But we don’t care!
It varies with temperature, the oil must remain viscous enough to keep between the two parts in contact, while remaining fluid enough to move freely through the engine.
To measure the grade, the oil is brought to a certain temperature, then the time it takes to pass through a standardised orifice is measured . I pass over oil characteristics, grade , … Bla-bla-bla ...

On our assemblies, we need two kinds of lubricants.
-The one used to lubricate the parts outside the motor; bearings, slides,..... In short, all that must rub without gripping, pinchhing, and facilitate the sliding of parts in contact at moderate temperature A sewing machine oil is too fluid and quickly loses its properties with heat; it is quickly evacuated. A lost-consumption olive oil might be suitable if it wets all the parts in contact, but a SAE30 engine oil will hang better on the metal, because it is made for that!.

-The other place we have to pay special attention to is the inside lubrication of the moving parts within the steam environment; sliding valves , segment rings, pistons/cylinders.
At this point we must take into account two things:
Bring just enough oil to the parts in contact and create just enough emulsion to hang on. In order to avoid excessive consumption, an 80/140 SAE will be suitable .
Avoid having an oil that degrades and loses its lubricating properties due to temperature. A Grade 120 @ 140°C will be viscous enough and will guarantee this oily film between the rubbing parts,
Since the temperature is 133°C @ 3 bar (gauge) in the engines, the oil must not degrade with the temperature.
For convenience, it can also be applied to moving parts outside the engine, as these parts will be  hot : +/- 50°c measured on the crankshaft.. We must not forget, either, that unlike a conventional engine, the oil only passes through . A bit like on the chain of the chainsaw. There’s no point in overpricing oil.



What quantity to use in our steam plants ?
From my experience and tests that I have done, I would say that 1cc of oil for a 5cc engine running for 45min at 3 .5 b abs makes the job.
You may obtain diferents figures depending of a lot of factors , but as long as there is a drop of oil passing by in the condensates , that will be fine.


The position of the oiler:
Two choices:
Just before the control valve if the boiler is equipped with an isolation valve. This makes it possible to lubricate this valve at the same time.
After the control valve and just before the engine if the boiler is not equipped with an isolation valve. This is to minimise the return of oil to the boiler when it cools down: depressurization = suction.



I have a good friend of mine claiming that he does not see any advantage of an oiler for his steam engine. That works the same , he said !
I made a test with him , with a Prony 'sbrake to show him the difference in torque and RPM with and without oil.
He saw it and shyly admitted that the engines runs better with oil, but ….. he decided not to use it !
What I can do my « fliend » ???


Below a brake of Prony that I used to compare the power of engines.
One end of a wood is cut along and leaves a round shape to hold the crankshaft. The spring tension can be adjusted with the control knob by pinching more or less the end of the crankshaft.
The tin string wounded around the end is to counter balance the weight of the adjusment knob assy.
There is a needle at the other end to push on the scale .
The torque in Newton by meter is obtained by multiplying the lentgh « L » (between the needle and the center of the crankshaft) by the force « F » (read on the scale).
1000g = 9.81 N ==> roughly 10 g = 0.1 N.
It can be converted in Watts then , for those who likes it better !
From then, you find out your engine power, you can make comparaisons between some, and at least, you'll have a number to prove what you say.


Note :
-Remember that the power consumption of the brake is converted in heat. So with a more powerfull engine you may burn the friction contact and have erroneous readings. …. if not fire !:-0.


 73 
 on: Yesterday at 01:06:38 PM 
Started by zooma - Last Post by zooma
Thanks Chris,


I am back home today and looking forward to seeing if the white PVA that I used to glue the bulkheads has dried OK and penetrated into the wood as it usually does.


The "fillet" of white PVA (still wet) that can be seen in the hastily taken pictures (that I took as I dashed away to the caravan)  is something that I have always applied around unseen but important joints. 


PVA and Aliphatic adhesives give a slightly more "flexible" bond than other types of adhesive and should survive the rigours of regular power boat use better than some of the others.


I am tempted to use super-glue at times - especially when I would prefer a "fast fix" to secure things in place that I can't easily clamp securely and are likely to move during the drying process if they are not secured adequately.


Super-glue should be OK on all joints (?) and I know that when I am making a stand I always use it to get a fast hold before I nail or screw in a mechanical fixing to support the joints, but soft some reason I don't trust it anywhere on my new hull builds - unless it is impossible to use PVA/Aliphatic adhesives.


Does anyone on Mayhem build wooden power boats using only suer-glue?.......and if so, has there been any problems with bond failure after extended and regular use on a performance hull ?

 74 
 on: Yesterday at 01:03:29 PM 
Started by Howard - Last Post by Howard
Hi Warspite ,
 I don't use my motor bike that much these days so like to give it a good run out now and then, I got most of what I wanted  just the 3x2mm half round he still not got thought so as I cleared him out of it last time using it for the swagging  should have some in two weeks time but I'll wait till half term then have a run out again, I have the Monkey Island deck and funnel I can do to keep me going and start on the doors and other detail things so it will not really hold me up for now, The sooner I get this done means I'll have up start cutting and slotting card again so no rush as I have enjoyed building in plastic again so have enjoyed a few weeks rest  from card. but thank you for still watching and keeping a interest in my build.
              Regards Howard.   

 75 
 on: Yesterday at 01:02:36 PM 
Started by GrahamD - Last Post by Colin Bishop
Quote
Colin - won't hollowing out the balsa make it more buoyant?

I meant externally by carving off a bit too much and introducing excessive flare.

Colin

 76 
 on: Yesterday at 12:53:21 PM 
Started by GrahamD - Last Post by zooma
Evening session at the lake last night, so I took the Huntsman. So much quieter with the replacement prop shaft.


I think I might have to add a tiny bit of ballast at the back, or try moving the battery tray backwards. The boat sits a little low at the front at rest, but almost leaves the water at full throttle. I noticed a couple of times as I crossed the wake of other boats that it momentarily lost drive, as if the prop was coming out of the water.
I suppose this could be perfectly normal for a relatively fast and lightweight boat that's sharing lake space with big lifeboats though?


I am also using modeboatbits M5 prop shafts and find they work well enough without the extra cost of ball raced shafts - although I will be trying a ball raced type in a future build to see if I can notice any difference.


Heaver boats and bigger boats generally handle the wake produced by other craft on the club lake better than smaller boats or lighter weight boats - but skipping across the wake with a nice performing model shuch as the Huntsman can be a lot of fun!

 77 
 on: Yesterday at 12:48:56 PM 
Started by zooma - Last Post by ChrisF
Hi Bob

Good to seeing it progressing and looking forward to seeing the hull taking shape.

Chris

 78 
 on: Yesterday at 12:42:18 PM 
Started by GrahamD - Last Post by ChrisF
They do have a tendency to sit a little bow down at rest due to the sleek shape of the bow providing less support. The full sized boat has the advantage of two big diesels and fuel tanks etc. to keep the bow up!

Colin - won't hollowing out the balsa make it more buoyant?

Chris

 79 
 on: Yesterday at 12:38:00 PM 
Started by GrahamD - Last Post by Koinonia
I found moving the battery back and a bit of testing really helped with the balance.  I use the same figures which are Bruder. My grandsons have Bruder toys which are 1:16.  EBay!

 80 
 on: Yesterday at 12:31:56 PM 
Started by GrahamD - Last Post by Colin Bishop
They are Bruder posable figures and I agree they make all the difference. There are only two who are really look the part in a powerboat though.

https://www.scalefarm.com/d-60006_access-farm-figure_bruder_bworld_man_with_blue_trousers.htm

https://www.scalefarm.com/d-60003_access-farm-figure_bruder_bworld_man_with_white_jeans.htm

You may be able to get them cheaper elsewhere but beware of p&p costs.

Colin

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