MalcolmX

car polish on the underside might make her faster too, or wax her like a surfboard.

i have a crafty idea for modifying my sponsons, i might try doing it in Styrene sheet; to get a really sharp edge

Rull

My friend, FSR racer , told me that he have tested sanding of bottom plane. He got up to 2 km/h plus on his FSR-15 with sanded bottom plane by a 240 grade sandpaper .
So polishing may get worse result.
For experiment try to move two pieces of glass with a water between them.

Rull

Thank you , Gerwin.

MalcolmX

i'm not sure about that; because racing yachts nearly always have gloss undersides, they rarely use matt anti-fowling paint; simply because it slows them down, this FSR racer might be going faster; because he sanded the underside bow to stern, thus adding additional ( microscopic) tram lines in the sponson; aiding the flow of water.

i asked my father 3 weeks ago which was faster, he said ``gloss hull is faster``, that's why racing boats always have their undersides scrubbed clean before races and are best kept out of the water etc.

ryan_t888

I'm a firm believer of scuffing > Smooth Finish

However, after several repeated attempts I can not say one is better than the other by true proven results. Even if you are racing, going to this degree does not seem neccessary but probably wouldn't hurt much.

Ryan

MalcolmX

i would say that gloss is better simply because it's a tougher/ more attractive finish, it's no big deal.

the important thing is to get that sponson the right shape

BACKEMF

Correct me if I am wrong but, large full size boats don't have nearly as much surface tension as a small model. Therefore adding the fine lines from sanding can help break that tension that just doesn't exist on full size.

MalcolmX

yes maybe.

Jeff Wohlt

This has been a big topic and yes, sanded hull is faster. Even a few of the big racing cats do it and now they have dimples like a golf ball in some areas. I have some video of CRC offshore cat with this. Also, the big hydros do this with a matt surface on the sponson hulls.

It is about how the water release from the surface. Slick keeps a sheet of water on the hull. It is true and this has been proven.

gonggongboy

We should open a seperate poll and see what other RCU'ers think is best. Or if they have heard of other bright ideas.

MalcolmX

good, because a matt/ sanded paint is far easier to maintain than a shiny underside, especially if you have to repair a damaged hull, in fact; i'll do the whole underside in matt grey primer and cover the sponsons with epoxy/ fine sand, i'll redo my illustation and take a look at it right now. it looks great, even better than white, i've always liked ``Battleship`` grey anyway

i've used epoxy and sand before, it produces a rock hard finish, in fact; once it's on it's virtually impossible to strip off , this tells me that i'd better be very careful, it might be best to mix the sand into the epoxy and not too much of it either; and carefully paint it on.

because sprinkiling sand onto a wet surface wont work, its density will be far too much, just like a sheet of rough sand paper, it needs to be more like a grain of sand every 5 mm or so

Rull

Try to see it from the other side.
The steped hulls have advantages only on a high speed, but they are worse on a slower speed , where unsteped hull better.

MalcolmX

that's ok, i'm interested in high speed only !!!! the faster the better

Rull

Motor`s water-cooled cans (not finished) 36 mm inner and 40mm outer diameters.


Motor`s mount plates

Rull

So guys, need advice about motors mount. Do you like the place of mount? I want to have much space for CG adjustment by the batteries. The batteries will be placed in the bottom of sponsons.

Gerwin Brommer

You CAN'T determine the position of the motors without all the stuff that needs to be in the hull !
Put everything in the hull at about the right places.
make sure you can move the lipo's to change the CG.
The space left is meant to be for the motors.

MalcolmX

getting this right on mine will be hard too.

but your cat is looking very good indeed, very neat and tidy with good attention to detail.

gen3v8

My Feedback: (1)

I found this thread interesting. Because i built one last week and i`m not up to date with all this electric gear. Heres some pics and a video of the 2nd run.[youtube]http://www.youtube.com/watch?v=ZCw_xu3bKdM[/youtube]

Rull

Hi
Good attitude of cat! Congratulations!

Could you show me some details of the interior? servo placement and mount.
What is the setup, weight?
I think the outrunners are to hot.

Rull

It is too easy make placement having all necessary stuff. But I haven`t battery now. No reason to buy them in winter.
I will buy them in spring from fresh lot.
And Li-Po can be 4S or 5S. So in this case I placed motors as closer as possible to transom. The left space for batteries.

gen3v8

My Feedback: (1)

The weight is 3.45kilos It has twin hb3650 hobbymate outrunners on 100a flyermate esc and 8x2300 a123 per motor. 4mm flex shafts with modded x442 l&r props. I have only ran the boat 4 times and i`m a bit unsure of it but it does handle very well I think. Need to learn much more.

Rull

Here the marker of 33% of hull leigh

gen3v8

My Feedback: (1)

Nice carbon/kevlar composite. Should i strengthen mine?

Rull

Thank you for the fotos. I should think out about vertical servo mount. I want wired pushrods.

It is 160 g/m2 carbon-kevlar on a Larit-285 epoxy. I didn`t want to make reinforcement because it sould be maked on a molding stage but one man persuade me to do it. And he was right. The hull now is hard no twists. It is additional reinforcement of gluing of bottom and top part of hull. Kevlar is leyed up to entrance of deck. Scratch surface well before gluing.

gen3v8

My Feedback: (1)

Ran my cat again today and got some good results.
PS the motors are hobbymate b3650 1700kva.
5cell 2300ma x3.2volt 73.7km/h. Just to clear the grease in shafts a bit.
8cell same batts 105km/h...65.2mp/h. Very stable on glassy water, sorry dunno the terms too new into boats