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Author Topic: Miss Britain 3  (Read 8505 times)

dadandlad

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Re: Miss Britain 3
« Reply #25 on: February 04, 2011, 08:30:23 PM »

Mart im not trying to reinvent the wheel and yes i agree a strimmer engine and flex cable would be a lot easier i just do not have the height to fit a engine in the centre of the boat,the original model only just managed to get a 700 bb in there.

As a matter of interest where should the balance point be.
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phillnjack

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Re: Miss Britain 3
« Reply #26 on: February 05, 2011, 01:30:51 AM »

Balance point of the average race boat is just under a 3rd of the length of boat.
Now to be honest,i cant see you getting anywhere near the correct balance point,even if you use the waterline length .
By putting a 23cc engine or even bigger in the very back of the boat your liable to sink it rather than get it on the plane.

If i was you and i wanted to us such an engine then i would build the sides of the boat a bit bigger so it does accomadate the engine near
to where it should be.
The design of the hull was very different to todays powerboats i know, and the centre point of balance was probably different as well.

I think that youl want a balance point atleast 10 to 12 inches from transom to get any sort of performance without huge problems.

This is where i have had big problems with strimmers and chainsaws in the past, size and weight issues.

i wish you lots of luck with your build and do hope it turns out right for you.


phill   :-)
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martno1fan

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Re: Miss Britain 3
« Reply #27 on: February 05, 2011, 05:52:45 AM »

Mart im not trying to reinvent the wheel and yes i agree a strimmer engine and flex cable would be a lot easier i just do not have the height to fit a engine in the centre of the boat,the original model only just managed to get a 700 bb in there.

As a matter of interest where should the balance point be.

Not trying to put you off m8 just trying to help.
I think by the sounds of it your boat is too small for this type of engine but not having seen it i dont know.
I honestly think electric is your best option,either that or nitro.Balance point is usually arround 28-32 percent of the boats length on most fast boats.
Mart
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Roadrunner

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Re: Miss Britain 3
« Reply #28 on: February 05, 2011, 08:26:22 AM »

I have to agree with Mart on this one, that a nitro engine sounds like a better option to use over a strimmer/chainsaw.

They are compact in size and believe it or not just as powerful as a strimmer engine in a boat!

The advantage is there is no conversion needed of this type of engine as all parts to are available off the shelf at reasonable prices ( water cooled cylinder heads, motor mounts, flywheels and couplings.)

There cost would be about the same if you purchased 2nd hand as a strimmer engine would be or even new you can pick up a size .12 for around 60 up to sizw .15, .18, .21 & and the .28 size can cost between 100- up to 250 ( i say .12 bla bla bla sizes as that was the lingo in nitro sizes from my race car days not sure if that's changed over the past 10 years to engine size in capacity 23cc etc)

Going by old money  {-) i would have though a size 12 or 15 would be more then enough to propel a boat along quite nicely.

Only bug is you will need to to pay out for glow plugs and its starter, tuning is temperamental but once sorted they run for years with little modification to that setting,  biggest bug of them all is fuel cost, nitro mix i think last time i looked was 22 a gallon think VAT has pushed it up a bit more now so worth shopping around.  Be sure you keep to the right nitro mix , 15% 20% 25% 30% as fuels vary depending on there use, my 10th scale rc car (touring) ran a size 21 on 20% nitro , where as my 1/8th buggy ran 30% in a 28 size engine.
( i ran higher nitro content on the buggy to get the most out of the engine in regard to hill climbing events, and rpm.)
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Arrow5

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Re: Miss Britain 3
« Reply #29 on: February 05, 2011, 08:52:52 AM »

I tend to agree with Roadrunner on the glo engine option except size, a .12 wont hack it in a 4ft hull .  A  .60(10cc) would be more like it. The cost of glo fuel is in the nitro additive. Most glow engines will run very well on cheaper low or zero nitro, 5% is a good option.  A four stroke with  castor oil sounds better and has that smell of the period scale engines.  Picture show the problem of fitting any engine anywhere but in the scale position , aft under the cowling. A "side-winder" mounting would still be tight at the front but could be an option. Start collecting the litho plates guys, looks like a lot of tin-bashing coming up, not to mention the rivets. (pic is real boat in Maritime Museum Greenwich but doesnt show how little depth the forward hull has.)
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..well can you land on this?

martno1fan

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Re: Miss Britain 3
« Reply #30 on: February 05, 2011, 11:54:07 AM »

I have an old sc .60 aero engine with a marine flywheel somewhere if your interested,it ran well when i tested it a cpl years ago but its been sat since and never used in a boat.If i can find it your welcome to it for cheap ,and you could buy a water jacket for it cheap,the marine version is the same engine just with a water jacket i believe.This one had some damage done to the mount part as someone tried drilling out the holes but it wont be an issue and could be fixed to look nice with jb weld,ill have a look for it and post a cpl of pics if your interested,might even have a starter belt somewhere.
Mart
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phillnjack

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Re: Miss Britain 3
« Reply #31 on: February 05, 2011, 08:54:57 PM »

Yeah this boat needs atleast a 60 or maybe even a 90 to get the best performance.
and i agree a .12 wouldnt get it even making wash let alone zooming across the water.

you have to remember this was a record breaking speedboat, so it needs to look pretty quick.

I think the chainsaw idea was good, if the boat would of allowed it to fit.

As for power, the 10cc nitro mart is talking about will kick out about 1.5bhp, power to weight is very good


but if the chainsaw does go in, i would like to know the results


phill
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dadandlad

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Re: Miss Britain 3
« Reply #32 on: February 05, 2011, 09:11:13 PM »

Cheers chaps
If i was to use the chainsaw engine it will sit with the head just behind the cockpit opening,I think whatever engine is used this will be the case as you will hopefully be able to see in this picture.


Today I machined the barrel and made the water jacket so what im going to do is finish the engine conversion weigh it and post dimensions etc




Arrow 5
Four stroke would be very nice and as you say a better sound and yes the smell and oh dear the price,as a teenager we used to sit in my mates shed flicking castrol r on a 3 bar electric fire  :-)) I think the modern equivalent is glue %%
As Arrow 5 says start collecting the litho plate or does anyone know of any suppliers   






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martno1fan

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Re: Miss Britain 3
« Reply #33 on: February 06, 2011, 08:05:54 AM »

Ok im in cmon lets see how you get on  ok2,i hope it works out well for you i like your attitude good luck with it  :-)).
Mart
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dadandlad

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Re: Miss Britain 3
« Reply #34 on: February 06, 2011, 01:32:16 PM »

Cheers Mart  :-))

Now for water cooling question
I have planned for water cooled head,intake manifold and exhaust manifold will i be better off with a onboard electric pump and a manifold to distribute water to each part or a water scoop or scoops

Nearly forgot my second question,I see some models run with a velocity stack on the carb intake is this needed and what are its benefits

Cheers Mark
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martno1fan

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Re: Miss Britain 3
« Reply #35 on: February 06, 2011, 03:14:50 PM »

If your running a clutch then id go with a pulse pump,you can tap the plastic insulator block for the carb to pick up the pulse from the motor which will work the pump,you will also need pickups.What happens is the pump works when idling but as you get moving the water pickups take over.The velocity stack isnt needed in a boat in fact some say it harms performance as you need every bit of air getting to the carb you can ,most of us throw them away to be honest.
Mart
http://cgi.ebay.co.uk/WATER-PUMP-twin-circuit-rc-model-boat-Zenoah-gas-/150556837772?pt=UK_ToysGames_RadioControlled_JN&hash=item230de3078c
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dadandlad

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Re: Miss Britain 3
« Reply #36 on: February 06, 2011, 08:51:39 PM »

Cheers Mart
I did not know they did anything like that
Today i have made the carb intake manifold which now needs drillings adding for water cooling and a tapping for the water pump
Got a bit excited today and weighed all the components and it comes out at 1460g few bolts to add to it but should still weigh under 1.5Kg

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samuelmerry

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Re: Miss Britain 3
« Reply #37 on: February 07, 2011, 10:28:09 AM »

If your running a clutch then id go with a pulse pump,you can tap the plastic insulator block for the carb to pick up the pulse from the motor which will work the pump,you will also need pickups.What happens is the pump works when idling but as you get moving the water pickups take over.The velocity stack isnt needed in a boat in fact some say it harms performance as you need every bit of air getting to the carb you can ,most of us throw them away to be honest.
Mart
http://cgi.ebay.co.uk/WATER-PUMP-twin-circuit-rc-model-boat-Zenoah-gas-/150556837772?pt=UK_ToysGames_RadioControlled_JN&hash=item230de3078c


What you say about getting less air in with a velocity stack/ram pipe is wrong, having one fitted will increase air flow not decrease it, perhaps it is for a different reason???
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martno1fan

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Re: Miss Britain 3
« Reply #38 on: February 07, 2011, 12:01:22 PM »

Its not wrong mate think about it these motors are ran inside an enclosed boat so removing it helps,they do no good inside a boat thats why everyone throws them away.Only people that use them are the car guys not many boaters that i know of.Buy any modded zenoah 260pum from any top builder and you will find the motor comes minus the velocity stack as they know theyre not needed.
Mart
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phillnjack

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Re: Miss Britain 3
« Reply #39 on: February 07, 2011, 01:33:21 PM »

Velocity stacks dont help unless loads of air flowing straight past them.
They then act like a vacum and drag air into to the carb from passing air.

In an enclosed boat they will not help at all.

Old seasull outboards, the most trusted engines in the marine world have velocity stacks on the carbs, but if
you look where the carb is placed youl see why, air goes past the stack when in normal use.
without the little stack you could get opposite vacum and not enough air to the carb.
some of the later models had a carb cover, these were slightly quieter due to cover and less performance.

But if the engine was enclosed, like in a lot of outboards then the stack would be no use at all.

Ive tried stacks on many full size outboard engines with clamshell type covers, they realy dont work.
Volvo penta 70hp came out with them on the first 70hp model and then they took them off .
everyone i know who had very early vp engines took them off and the performance went straight up.


Mercury outboards had them on their racing outboars back in the 60's, but this was on uncovered engines.
even the latest 350hp models dont use stacks, they would lose hp.

On big v8 custom rods they use velocity stacks when the pumper (carb)is above the bonnet or when using ram air vents.
Also when using complete open engines like on model t buckets.
when not using ram air and just covered engines , no stacks

V8 Range rover engine uses stacks in the plenum chamber, but take them off and youl see big improvement on
performance and fuel consumption.



phill
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samuelmerry

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Re: Miss Britain 3
« Reply #40 on: February 07, 2011, 05:14:59 PM »

Ahhhh I see, I have only ever worked with ram pipes on cars where there is air flow or an air box fed with air from the forward motion of the car.


By this then if you could encourage greater air flow past the velocity stack on a boat you would see greater performance. I am sure this could be achieved using a duct of some description.....
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martno1fan

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Re: Miss Britain 3
« Reply #41 on: February 07, 2011, 05:20:02 PM »

The problem is Samuel that on a boat you get water spray especially when following other boats so that could be an issue,one way arround it would be to use a deflector of some kind before the air gets to the carb to stop the water but i think if velocity stacks worked all the guys running SAW events would be using them.
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phillnjack

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Re: Miss Britain 3
« Reply #42 on: February 07, 2011, 10:54:04 PM »

without rapid air flowing directly over a velocity stack it dont work.
This is the reason its no good in an enclosed area.

if you look at a v8 with a nice high offenhouser inlet manifold with holly 800cfmn carbs sticking out of a
bonnet or open engine of a custom car, youl see velocity stacks.

But if the bonnet is a conventional closed one with no ram vents youl see big flat chrome carb and filter box.

also side draught webbers and del orto's used stacks, but again the name says it all  side draught.
These needed plenty of air directed at them.


phill ok2
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dadandlad

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Re: Miss Britain 3
« Reply #43 on: February 07, 2011, 11:42:52 PM »

Cheers boys no need to make one of those then :-))
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samuelmerry

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Re: Miss Britain 3
« Reply #44 on: April 19, 2011, 01:05:18 PM »

Any news on the progress of this build? sounded interesting......
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