masalai's model movie

Hi folks,
<edit> Shortest video (not small - 13.4MB) is posted here http://www.boatdesign.net/gallery/showphoto.php?photo=9889
Time for revenge and to criticise the criticizer. I have 3 QT videos I made with a Nikon coolpix S3 pocket mini camera, held by wobbly hands. Camera is autofocus - sometimes.

I taped a gps to the roof which read max speed 4.2knots, 2.3knot moving average for 250 metres over 10 minutes in the water with some stop time (didn't think to record moving time).

I don't know how to cut out the rubbish where a) I nearly slipped over several times with waving hands. b) I nearly fell in the water whilst getting up from doing a low shot of under the bridge-deck c) could not turn the camera off. bloody small buttons.

I will attempt to post the smallest one. If someone would like to fix the files, PM me and I will endeavour to send them directly to your own email address.

the file names are
DSCN1538.mov of 49.8MB
DSCN1539.mov of 13.4MB
DSCN1540.mov of 41.5MB

Regards

 

Brian
The video files are all too big for Boatdesign. 10Mb is the limit.

Set up a YouTube or Google Video account and post there. You can also get free or low cost converters that will reduce the file size.

Also the majority of email servers limit files below 10Mb so there will not be too many who you can email the files to.

What type of GPS were you using? You can download the track from most of them. This will give you a better idea of performance.

If it is 10kg it must be sitting below the waterline. Have you got some photos of it in the water.

If you give me the prop measurements I can do some back calculation.

What voltage and current were you operating at?

Rick W.

 

Well Rick, thanks for the info. It seems that smaller file was accepted and is in my gallery now. I can download 800 plus MB but it takes about 8 hours on my snail-mail paced broadband (that is my bigest so far). I haven't tried the other way beyond about 20MB.

The video files give 640 x 480 at 30 fps. when I play them.

I need to edit the files first, no way for me yet. (also no great interest)

It appears that boat-net has some VERY powerful automated systems for images etc. I am most appreciative of the excellence in online resources.

I would not mind making donations every now and then, but I will NOT give creditcard info online EVER.

GPS is a garmin gps60 small monochrome hand-held.

model weight is pushing the waterline, but not by much. The bows are about right but the stern should be half way up that flat extension/step thingy. The Chamberlin idea was to pivot loading so the stern changed very little and as fuel and other things were added, the bows settled to the design WL. Model is a bit in reverse of that.

I may have to get some experienced advice before I start to work on next phase/stage. I have to specify internal rayout and things to go in by priority/need down to likes "if", so weights can be calculated then re do below waterline to reflect this and build weights.

I am sort of happy with concept, now to fix the design criteria and accept those specifications ready to present to a NA/NE for design finishing ready for builders.

2 x 40mm dia screws powered by "Drake Horse" Speed 600 series from 3600mha x 6 7.2V NiMH batteries - reading straight from the motors & battery pack. Don't have current info but it is heaps! Both rotate in the same direction. Nearly forgot, the props were sucking quite a bit of air. I will try some "bogey" fix then have another speed trial.

I do not have the download software on linux yet for the gps, a low priority to-do at the present.

 

Brian
It is very nice. I like it. Surprisingly good since it is overloaded. A pity you could not keep to scale displacement.

Scale speed is 13kts and waves well developed as you would expect. Michlet can provide wave patterns and these are always useful to verify that it is close to reality.

This boat should do better with small bulbs in the bow as there is a lot of water being lifted.

You could also taper the flat aft sections over the rudders to canoe shapes as well because there is energy going to waste in the turbulence off the square stern.

You can buy Multimeters from Tandy that go up to 10A. They cost AUD16. You could mount this and take a reading is it passes by. I expect with a little effort you could calculate hull resistance to within 10% from this model.

Rick W.

 

Thank you Rick, can the bow be fixed a bit better without bulbs? That stern is not working as well as the Chamberlin C10 (real size images) in my gallery.

Have a look at the pencil lines on the closeup from under the stern. I was thinking of extending the main underwater section to there and make it a lot finer and giving a little more volume/load capacity to the whole hull.

that flat section then is useful to smooth the exiting waters for a transom mounted Levi surface full cavitating screw (xrudi has a members gallery here and operates the Levi base in Penang) above it and rising from the last vertical bit will be the hull transom to carry the Levi mounting arrangement.

I am at the present keen on the levi/surface screws because of the bigger wheel, potentially improved efficiencies, am I reading **** from external sources, or on the better track?

I tend to write very forcefully, it's how I think. I am still very open to change in a soundly reasoned presentation. I thought I could maximise hull volume with a squarer shape (in hull section) and blunt ends. Probably have to accept finer entry and exit but not very much I hope? If it has to be done it has to be done. It is a compromise between shallow draft capability and narrow efficient hulls and able to carry two tonnes of fuel for range at 12 to 15 knots flat seas. (desire at least 2000miles, and would call absolutely MAGIC - 3000 miles, as a guess unattainable?) Is that asking too much. I like the Chamberlin efficiency challenge at bottom of page http://www.icecat.com.au/trial.htm

 

There are other options to the bulb but I think the bulb would suit your speed range. It would not need to be very big. The nose would not need to extend beyond the overhang of the bow.

You have a baseline now so you can make one change at a time and see what benefit you get.

I would change the stern first as it is generating a lot of turbulance. The pencil line shows what I was thinking of. I would try to ensure the rudder is covered.

The stern in front of the prop does not have as much taper as Godzilla produced.

I have only played with human powered surface drives. These are much less efficient than a good prop. Surface drives gain a real advantage at speeds where apendage drag is significant. I have not seen any data showing that they get better than 70% efficiency. With the right prop you should expect much better efficiency than this and your pnly appendage is the rudder, which could be smaller than you have. In any case it will not offer a lot of drag at 13kts. I can do calcs on it if you want.

From an efficiency point of view you should aim to fit the largest diameter prop you can and keep the prop shaft horizontal. I have attached a JavaProp screen dump for a 550mm prop showing 82% efficiency for the original Godzilla hull at 14kts. You could go to a smaller diameter and shroud the prop to keep efficiency up. This might end up with a good result.

Power at the prop shaft is 16kW for each motor. If you do not oversive then you might achieve this with 18kW at each motor. Twin Kubotas should produce this for 11l/hr combined. So you use less than 1l/nm!!! This has no allowance for windage or sea conditions. It seems the 2.5l/nm for the 36hr trial should be achievable.

The model looked nice. With a bit of work I think you could get a really efficient boat.

Rick W.

 

Thanks a lot rick. You may be a bit ahead of me. Let me catch up a little and get my act together. That stern treatment was maintaining the "vertical" fin shape to the transom. Eliminating the existing rudder & screw.

I would look for a bigger screw, Levi Surface Drive 170 - 150, ( http://www.boatdesign.net/gallery/showphoto.php/photo/2458/ppuser/1490 ) are all for converted local Malaysian boats that weigh about 1.5 or so tonnes I think, for connection to 50hp plus diesel truck engines.

 

Like I said the best efficiency I have seen from a surface drive is around 70%. The Malaysian boats probably use them for their simplicity and low draft.

The current set up with your cat is ideal for a standard prop. There is no support strut required and the prop shaft can be aligned horizontal.

If you are keen to try the surface drive why not give it a go on the model? I think you would find it hard to match the current set up.

Rick W.

 

Thank you Rick, Sometimes I am a bit thick. I didn't quite grasp what you were getting at before.

 

Hi Masalai

Regarding your Pm here is a picture of one of my drives.

 

You're happy with that? - sidewinder? What weight does it push? Where is the thrust bearing?

 

Its not a Levi Its my own design. The hull holds everything. I don't need exhaust injection to lighten the engine load.

The thrust bearing is in the gearbox ZF 630 down 8 degree 2.5:1

The boat is 14 tons cruise KTS 17 --- 3400 RPM

23kts 4000 but can go to 4200 Never given it max.

Lot of prop slip there could do with 26inch Dia props instead of 24

Pictures of full hull in slings posted in shafts thru the transom.

Let me know if you cant find it.

 

Thanks very much frosty

 

Thank you again very much Frosty. I read , I saw, I understood.

Did you have to add those little rails parallel to the centreline of the hulls, either side, but further out than the line of of the screw tips?

 

I dont know what you mean by that. Theres nothing stick out after the hull transom, exept a 1inch vacuum break which I had just fitted before the photo.

According to the Seafury site this is imperative. It did nothing for me.

I sometimes think that there is a lot of bull crap about Surface props to keep people from building something that looks so simple,---it is!! Its the prop thats different,--all you gotta do is get the right prop, place it and turn it.