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Author Topic: Power unit/s  (Read 3922 times)

john54

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Power unit/s
« on: November 02, 2007, 12:29:04 PM »

Just finished kitting out a boat i pick up g.r.p hull deepvee wood superstructure 43in x 14  5kg.
She had a 61 ic motor fitted cant use i.c on lake so fitted m.f.a 850 tryed running her on 12v 7.5 amp s.l.a also 14cell 3000s
props from 35 to50mm still not happy with her speed. I know shes a big lump!(see pics)
Am i asking to much from lecy motors ? How about x2 700/850s on gearbox to single shaft ?
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DickyD

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Re: Power unit/s
« Reply #1 on: November 02, 2007, 01:20:03 PM »

Just how big is she dimension wise ? :-\
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john54

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Re: Power unit/s
« Reply #2 on: November 02, 2007, 02:47:05 PM »

Hi
Size loa 43in beam 14in height 10in weight without battery/s 5.2 kg.
People @ club seem to think the hull might have been a halmatic test tank model @ one time very well made.
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DickyD

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Re: Power unit/s
« Reply #3 on: November 02, 2007, 03:05:44 PM »

What is a 14cell 3000 John ? Just noticed that.
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John W E

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Re: Power unit/s
« Reply #4 on: November 02, 2007, 03:13:29 PM »

ooooo there marra, this is the other John  O0

I am sure its a NiCad battery pack.   He may be running this alongside his other gell battery or using them separately.

I think  ::)

by the way the other John, John 54, are there are photographs of the inside of your model to give us some idea as to how its built.

john e


bluebird
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DickyD

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Re: Power unit/s
« Reply #5 on: November 02, 2007, 03:26:04 PM »

If its a battery pack it would at 14 cells be 16.8v . Dont sound right to me.
What is wrong with the speed, does it plane ? does it just not appear to be fast enough ?
10mph is the equivalent to approx 40knots [thanks cdsc123] scale speed.
Think we need a bit more info please.
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john54

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Re: Power unit/s
« Reply #6 on: November 02, 2007, 03:55:59 PM »

Heres more pics of boat & packs i have tryed.
She does semi plane (about half the hull) & leaves a very big hole in her wake!
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Stavros

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Re: Power unit/s
« Reply #7 on: November 02, 2007, 05:16:48 PM »

If you are using a MFA 850 you should be on a 55mm 2 blade prop running 12v gel cell.I have a Sea Queen which has the identical motor,and she planes with ease.The only difference is that my motor is water cooled and probably the Sea Queen is also heavier and I use 2 x 12v 7amp gel cell batts

Stavros
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john54

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Re: Power unit/s
« Reply #8 on: November 02, 2007, 05:33:15 PM »

I had a sea commander next one down to yours That went like stink with a 700.
But this one has a much deeper vee stern profile that might be why she struggles to get up! correct me if iam wrong.
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cdsc123

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Re: Power unit/s
« Reply #9 on: November 02, 2007, 06:35:26 PM »

How about trying trim wedges and/or transom flaps?
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john54

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Re: Power unit/s
« Reply #10 on: November 02, 2007, 06:43:22 PM »

Wont trim tabs bring the bow down ?
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cdsc123

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Re: Power unit/s
« Reply #11 on: November 02, 2007, 06:56:41 PM »

Yes, your comment about a big hole in her wake leads me to believe your model is "labouring".
Can you get the battery weight just a little further forwards? (not too far though).
Once she pops up on the plane properly you should see an increase in speed, and once you get the running trim sorted, as Stavros says, you could experiment with larger props too. You may then however begin to suffer a torque reaction, with the boat trying to lean over to run on one of her V-bottom flats.
If you have trim tabs you can go adjusting the running trim and also dial out the torque reaction too.
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john54

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Re: Power unit/s
« Reply #12 on: November 02, 2007, 07:41:55 PM »

Thanks
Got some alloy plate Will make some tabs (2in) be enough?
Down lake on sunday so will try all all things you kind gentlemen have suggested.
Will take pics of her running so you can see the results.
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John W E

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Re: Power unit/s
« Reply #13 on: November 02, 2007, 08:27:20 PM »

hi all

a quick explanation :

John 54 - the hull you have is obviously based on an offshore power boat hull of the Surfury type hull.   Medium to deep 'V' section.

Normally, MTBs, Picassa, SeaQueen's the hull's 'v' viewed from the stern is shallow to medium.  Meaning, from 0 degrees flat from chine to chine, up to 13 degrees from keel to chine.

Deep Vs go 13 degrees up to about 17-18 degrees.

The shallow 'v's vessels come onto the plane quicker and with less power.  However, in the life size boats, they were prone to slamming in heavy seas.  To counteract this, they adopted the type of hull which you can see in the Picassa type hull.  This is where you have a very narrow entry point at the bow and it flares out to the medium 'v' approximately half way along the hull.

Now, when the guys were doing the offshore power boat racing in the 60s and 70s the flat 'v's hulls tended to self-destruct.  So the next step was to increase the angle of the 'v' from 13 degrees upover.   This requires a lot more power to bring the vessel onto the plane.  You will notice on the hull you have, John54, the bow cross-section profile is not narrow, but, full 'v' and this 'v' carries on at the same angle all the way on to the transome.

You also have 'spray rails' on your hull.  The original idea of these was to reduce 'wetting areas' on the hull.  In other words to throw the spray away from the sides of the vessel and therefore reducing 'water-drag'.

Now we have explained a little bit of the theory side of it, to try and solve the problem.

The hull looks a fairly substantial built fibre glass hull and it looks as though its been used in its past life with an I.C. engine for some sort of off-shore racing.

Suggestion of putting trim tabs on the back, may well work, but I doubt if it will. The reason I dont think it will work, is, it will bring the bow down and therefore increase wetted area to the hull. What you must do is try and keep the weight of your batteries down low, by using NiCad packs and also, as has been mentioned, use a bigger prop and water-cool the motor.   

What you should be aiming for is what is known as quarter the hump  ::) sounds rude but....what it actually means is - if you can imagine a see-saw, the crest of the wave, where the boat is planing on is the 'A' frame support and the plank where you sit on, is the boat.

The bow of the boat should be 3/4 of the length away from the centre of the wave, so you only have your stern 1/4 in the water.

Hope this helps you - its a lot more difficult to explain than I originally thought  :D :D can draw a few pictures if you get stuck.

aye
john e
bluebird
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john54

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Re: Power unit/s
« Reply #14 on: November 03, 2007, 06:53:44 AM »

Hi John E
My G*d your the man!
Lots of interesting info there now i have some idea of what iam dealing with now.
Shame i cant use i.c because iam sure extra power will sort her out (was fitted with a 61)
Might think about a brushless sytem/gearbox when funds allow!
In the meantime i will play around with what i have.
Thanks again.

John
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john54

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Re: Power unit/s
« Reply #15 on: November 04, 2007, 02:18:01 PM »

Success ! (i think)
Down the lake to day (Southsea Hants)
First run (pic 1) s.l.a 12v 7.5amp tryed 45,50,55 props Oh dear no good.
2nd run (pic2) X2 9.6 3000s in series, 45 2 blade prop hull up revs up 20mins run time Motor just warm.
Happy with her now all thanks to you guys.
Also ran my fast lecy (pic 3)
A few other club menbers turned up with their boats (more pics!)

Cheers JOHN
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DickyD

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Re: Power unit/s
« Reply #16 on: November 04, 2007, 02:58:20 PM »

Nice one John, just about right. Great day for the lake ,it was good here too.
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john54

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Re: Power unit/s
« Reply #17 on: November 04, 2007, 03:19:22 PM »

Good day all round then!
See what i mean by BIG hole she leaves behind ?
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john54

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Re: Power unit/s
« Reply #18 on: November 05, 2007, 04:42:17 PM »

Me Again
Noticed shes heeling over slightly at full chat so have to keep correcting making her zigzag.
I think its torque twist. Smaller prop (45) = no plane 55 = more heel !50 = nice speed but heel.
So Gents way out of it ? trim tabs (size & material), weight distribution or chuck her on Eb*y ?
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martno1fan

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Re: Power unit/s
« Reply #19 on: November 13, 2007, 10:45:49 PM »

where does she balance? you need to balance her at between 25% and 30% of the hull length from transom.thats where i balance all my boats.these two are petrol powered ,ones scratch built from plywood running with a strimmer motor.speeds over 30 mph,the orange one is a zenoah 260 powered offshore mono and speeds well over 40 maybe getting towards 50 and hoping for over 50  ;D.your problem is your boat needs balancing then you might have a chance but im thinking you need more power to be honest.thats a heavy boat both mine wegh 18lbs or thereabouts loaded with fuel but i have the power to move it especially in the orange one in fact im carrying 4 lb of balast which will come out when weather permits.
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john54

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Re: Power unit/s
« Reply #20 on: November 14, 2007, 04:44:26 AM »

As you say she a big lump (17ib) all up. Fitted trim tabs running o.k now.
Cant use i.c on lake so thats as good as it gets !
Unless i go brushless with gearbox ? (arm & leg!)

Pics not very good taken with phone/cam
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martno1fan

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Re: Power unit/s
« Reply #21 on: November 14, 2007, 10:51:27 AM »

As you say she a big lump (17ib) all up. Fitted trim tabs running o.k now.
Cant use i.c on lake so thats as good as it gets !
Unless i go brushless with gearbox ? (arm & leg!)

Pics not very good taken with phone/cam
you could go with lipo batterys they are small lite and powerfull ,i think twin props would be a good idea with two motors.nimmh cells would be better by far than gelcells though.
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martno1fan

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Re: Power unit/s
« Reply #22 on: November 14, 2007, 11:58:59 AM »

hi again did you ever see simons rttl boat ? his was maybe a bit bigger than yours but it went very well he powered it with twin  graupner 850 turbo motors i think (water cooled) twin 3 bladed 54 mm props and 2x electronize esc,s 30 amp each i think.not sure on the batterys though but def nimmh i think.heres a vid of it not sure if hes sold it now  ::) if he did i hope he got a good price :o.
http://www.youtube.com/watch?v=oMwJ1y2mob0
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john54

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Re: Power unit/s
« Reply #23 on: November 14, 2007, 02:27:01 PM »

Hi Nice video & rttl
Have tryed gel/bat 12v 7.5 amp no good at all.
Now useing x2 9.6 3000 ni-mh in series 20v ish.
When pic were taken it was rough & windy she goes just as fast if not faster than that VERY nice rttl when the lakes calm.
Worked out c of g is 30% from transom About right ? Dont think i will fettle her anymore she will do.
Got the yellow f.e for warp speed ! ( still cant i.d her) see above pic  any ideas ?
 
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martno1fan

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Re: Power unit/s
« Reply #24 on: November 14, 2007, 04:17:26 PM »

sounds like its running ok then  O0 as for that yellow hull it looks familiar im sure ive seen one somewhere like it have you any close up pics of it and of the bottom of the hull?.
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