v_tolias

Do you Know what weight and dimensions should have a hydroplane if i want to use a .21 engine which have these features ?
* Type - 21 ABC,rear exhaust, pull start, (MARINE)
* C.C. - 3.46
* Bore - 16.6mm
* Stroke - 16.0mm
* Output - 1.9 (PS) @ 30000rpm
* Practical RPM range - 3,000~35,000
* Weight - 421g

e.g. weight 1800-2200gr
length 600-800cm
widht 300-400cm

The engine is this http://www.hobbybox.gr/details2.php?...pid=623&page=1
Thank you very much and sorry because i don't speak very good engilsh!!

Hydro Junkie

That english looked pretty good to me. On to the boat question, but first I have a question for you. Are you planning on building from plans, building a kit or buying a finished hull?
As for length, here in the States, we usually run a hull in the range of 77 to 92mm. As far as weight, you want ot keep the boat as light as possible. As impressive as those engine specs seem, the little 3.5cc engines can't really do justice to a heavy boat.

v_tolias

Thank you very much!!
77-92 mm or cm?I want to built a boat from plans...I would like the length to be almost 700 cm!How much approximately have to be the weight for this small engine?
Do you recommend to use a bigger engine with less rpm and bigger prop...SC 46 Marine for example haves max. 12800 only!!
What about OS MAX-32SX-M and MAX-21RG-MX?

piper_chuck

My Feedback: (12)

Looked good to me. In fact, it's better than many here who are native English speakers!

martno1fan

sc engines are whats known as sports engines ,all they are is modified plane engines thats why the rpm is low i have a .61 sc engine i modified from a plane and while she runs well in a v hull shes not super fast the specs are the same as the sc marine version though .get a cmb or an os marine engine if you want a fast boat.

v_tolias

I haven't find a CMB in greece so it becomes very expensive if i order one from Europe or US...
So it is better to prefer an OS... I have these options MAX-32SX-M and MAX-21RG-MX..The firts has these features:
Output 1.1ps/17,000r.p.m. Bore 19.5mm(0.768in.) Practical r.p.m.Range 2,500-21,000r.p.m. Stroke 17.5mm(0.689in.) Weight 423g(14.92oz.)
and the second these:
Output 1.7ps/28,000r.p.m. Bore 16.6mm(0.654in.) Practical r.p.m.Range 3,000-35,000r.p.m. Stroke 16.0mm(0.630in.) Weight 317g / 389g (11.18oz. / 13.72oz.)
The .21 i think that is more powerful and fast,isn't it?
The price is the same so my problem now is,which one is better???
Thank you again!!

martno1fan

shipping from us or china isnt expensive have you checked? i use china a lot try here for cmb they are expensive engines but they are the best.there are cheaper alternatives out there but hey os are expensive too.[link]http://stores.ebay.co.uk/rcworldwide-com_Boat-Engines_W0QQcolZ4QQdirZ1QQfsubZ11QQftidZ2QQtZkm[/link]
ps one company sent me things marked gift so no import to pay
smaller engines rev higher so you cant allways go by rpm id go with what others use for your boat?.a 21 isnt going to push a hull thats made for a 40 for example as it wont have enough torque.

v_tolias

OS MAX-21RG-MX and MAX-32SX-M cost in greece 185€=123£ and i have not to pay shipping while CMB 21 valvola costs £193.83+shipping...

piper_chuck

My Feedback: (12)

Since the .32 appears to be heavier and less power, I would buy the .21. Build the right size and keep the boat light, as Hydro Junkie suggested, and the .21 OS engine will do well. While CMB, Novarossi, et al are definitely more powerful engines, it's not clear that the extra money is worth spending unless you need the extra power, or your budget can afford them. There is also much to be said for starting out with a lower cost engine and only upgrading after you've learned how to setup the boat.

Edit: If you want to save some weight, choose the non-pull start version of the motor and buy an electric starter. It might cost a little more, but the boat will be lighter, you will get more reliable starts, and you will have less maintenance.

330T

ever since seeing one of these run i've wanted one. I dont have the time to build it so until i come by one built and cheep i'll just have to wish

[link=http://blazermarine.com/cart.php?m=product_detail&p=187]Blazer Marine Sport 20[/link]

v_tolias

The boat becomes enough heavy..Almost 2,5Kg without engine so i will need a bigger one..
I think
OS MAX-46VX-M(ST) W/40A CARBURETTOR
Displacement 7.45cc(0.455cu.in) Output 2.5ps/23,000r.p.m. Bore 22.0mm(0.866in.) Practical r.p.m.Range 2,500-28,000r.p.m. Stroke 19.6mm(0.772in.) Weight 445g(15.7oz.)

OR

OS Max 61VR-MABC
Output: 2.8ps/22,000r.p.m.
Practical r.p.m. range: 2,500~25,000 r.p.m.
Weight: 910g

The second one is much heavier(500g) and the more power that gives is only 0.3ps...
What do you think?
The price is almost the same!