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[rory]

Im looking to scratch build a deep v mono hull rc boat. I've never built an rc boat but i know roughly what i want. I like the idea of converting a 2 stroke strimmer / chainsaw engine engine for marine rc use but i need some (through the course of the project probably lots) of advise from you experts. Now, i have the option of getting a McCulloch mac 738 38cc (2Hp) engine or a Royobi 30cc (1Hp) strimmer engine (the one i saw had electric start option) for the same money.
I have seen that lots of people have managed to couple the drive of a strimmer engine to a flexidrive fairly easily, and manage to also utilise the clutch. Is this possible with a chainsaw engine? Is there any reason not to use the chainsaw engine? clutch wont be too heavy?

Also, im thinking of a boat around 50 - 60 inches, i know there are loads of variables but is anyone able to give me a rough idea/formula for length overall to beam for a typical deep v? V angle and free board to get the displacement about right? i plan to have straight sides parallel from the transom to the point where i'd bring them in to a point, ie not rounded/concave sides -  parallel length to length overall? Im fully aware im asking a lot without giving much indication of what i intend to build but for the time being i am really just looking for very rough guidelines to follow, perhaps from someone elses similar boat?

I will make a card mock up before committing to wood to check the shape ets............

Any help would be very much appreciated.

Regards. Rory

[Prophet]

Given that this may be the first boat you have built u are giving yourself a lot of headaches before you even start best bet is to buy a new or 2nd hand model IC engine they tend to be more reliable easier to tune ( stimmer engines some of the cheap ones don't allow for idle speed tuning (since there set for the equipment on the end of them already) some also wont allow leaning or riching the mixture for better rpm, and basically there a nightmare to start sometimes giving there pull starts.. imagine large stiff engine trying to turn over.. huge pull yank the whole engine out of its mount .. I'VE SEEN THAT.

you will find that proper model ic engines will go the job just as well

also u should remember that stimmer engines will not have the head connector to allow you to water cool them which u should look at in ic engines finding a new cylinerhead with the water intakes on a strimmer engine can be a nightmare to track down.
 many rc Ic engines have prebuilt water intakes ( if you buy a marine IC engine)

http://www.sussex-model-centre.co.uk/shopdisplayproducts.asp?id=65&cat=OS+IC+Engines

new ic engines size 12 are around the 60-70 quid mark 15-18 around the 100-120 and 21-28 are anywhere up to a few hundred pounds.

you should decide first out type of boat your building.

is it a racer? cruiser,? or one of those fancy power boats ? be aware that all ic engines go like the clappers even the little ones can move a boat EXTREAMLY quickly across the water on a single 40mm prop (check rpm)

some real advice... do some research on engines and there needs, look for replacement parts readily available and remember this is your first boat so don't get over ambitious keep it simple

find a boat plan of a hull .. start with that. the superstructure can be your own design but better to start with a plan of a hull similar to what you have in your mind making a hull up as you go along could be quite risky..

hope it helps

prophet

[rory]

This will be my first boat build - I have done some some research on engines but i agree i do need to do much more. . . . Unfortunately i am at sea at the moment (i work on ships) and our internet, my only research tool, isn't anything like as good as it should be. Its all low res for a start.....and slow slow slow.

Many thanks for the link - just the sort of thing i needed as searching for good sites is painstakingly slow on here.

My initial plans are to build something resembling an off shore powerboat, in fact thats exactly the sort of hull i like, but with a higher bow as i have never been a fan of boats where the deck slopes downwards towards the front. A bit of flare in the bow also would be nice but - thats me being even more over ambitious than i already am! So i'll forget about that this time round.

I want a boat to run in the sea (i live in the outer hebridies) so nothing that would be too scared of a little ripple or wave or two and ideally something that would go around the 30mph mark so i could chase it with a real boat!

I will give your IC engine suggestion full consideration - it would be a LOT easier to fit, use, get spares for not to mention lighter and higher revving but for the time being i wont write off the McCulloch engine completely (its £110 quid new and i get spare chain saw bits to play with..) its stock max speed is 12000 rpm which from what i see so far should be enough from a 2hp 2 stroke to propel my creation along....... If i can get the head in a lathe then i can machine off the cooling fins myself and either make a cylinder jacket liner or use an aluminum coil, probably using water pickup from a flush fitting on the underside of the hull. But im thinking a bit too far ahead again.

Do you have any suggestions as to where i might find suitable plans for a hull similar to what i've mentioned? Or any other suggestions on hull types? Many thanks for your help so far - its greatly appreciated especially while im stuck out here! Happy sailing.

[Prophet]

off shore cruisers are pretty simple on the hull design with good planning ability
 
maybe for your first boat try the fairey huntsman kit with the GRP hull or do what i am currently building the all ply construction.

starting with a kit first time out may be more helpfull since you have instructions to go with it untill you build your confidence on building boats.

the huntsman can handle choppy water quite well search for huntsman on here u will find many posts on peoples builds one using a single IC engine with very nicely built. its not quite a power boat its a cabin cruiser however check its history out 

try here for the kit
http://www.alwayshobbies.com/Boats/Radio-Controlled-Model-Boat-Kits/Miscellaneous-Radio-Controlled-Model-Boat-Kits/Fairey-Huntsman-31.ice

or if this is your thing
http://madabout-rc.co.uk/rcgasnitroboats.aspx
http://skyhunterhobby.com/#/boats/4535999209

for an outright power boat hull check this ...
http://cgi.ebay.co.uk/ORBITER-46-RC-POWER-BOAT-GRP-HULL-KIT-(-RED-)_W0QQitemZ190386426388QQcmdZViewItem?rvr_id=&rvr_id=&cguid=99ac1e6d1290a0aad2469bb6fe56310b

also trawl the net for free plans ..
Hope it helps
Prophet

[Prophet]

also try here for plans....
http://www.myhobbystore.co.uk/group/30/model-boat-plans-x-list/?source=87&gclid=CIzI-unhiKMCFRQ_lAodmEJQdQ
or some free ones







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send me a pm here with your email and i will mail you the plans should you not be able to download off here...

[rory]

Perfect. Thanks for the help, thats given me a whole lot to think about now! The Huntsman isn't what i had in mind really but it is a great looking model and i'll certainly be looking into it.

Thanks for the links too - as i mentioned before we have very limited internet access and as such some of the sites have been blocked or are low resolution so cant read them but i've made a note and will go for a second look when i get back to civilisation! 2 weeks to go....

Thanks again. 

[w3bby]

Patternmaker has a nice thread on converting a weedeater motor here http://www.modelboatmayhem.co.uk/forum/index.php?topic=24746.0.

Weedeater/petrol engines will give you a generally trouble free start, relatively easy to set up, keep running and with low running costs.

A selection of plans for boats can be found here http://www.modelpowerboat.com/forum/downloads.htm. You have to join to download but the forum is good for advice as well.

[Patternmaker]

Given that this may be the first boat you have built u are giving yourself a lot of headaches before you even start best bet is to buy a new or 2nd hand model IC engine they tend to be more reliable easier to tune ( stimmer engines some of the cheap ones don't allow for idle speed tuning (since there set for the equipment on the end of them already) some also wont allow leaning or riching the mixture for better rpm, and basically there a nightmare to start sometimes giving there pull starts.. imagine large stiff engine trying to turn over.. huge pull yank the whole engine out of its mount .. I'VE SEEN THAT.

you will find that proper model ic engines will go the job just as well

also u should remember that stimmer engines will not have the head connector to allow you to water cool them which u should look at in ic engines finding a new cylinerhead with the water intakes on a strimmer engine can be a nightmare to track down.
 

Not strictly correct most strimmer or chainsaw engines make very good marine engines for race or sports use if converted correctly.
I have converted many and found them to be extremely reliable and easy to tune, average rpm around 6 to 7000 this can be improved considerably with porting and fitting larger carburettors.
If you have access to a lathe its quite easy to fit a Zenoah water cooled cylinder jacket.
Some modelers fit them as standard air cooled which is fine with an open top boat.

Most IC engines are converted from aircraft engines, very few are purpose built for marine use such as CMB

[rory]

Thanks for the help guys - great forum. I'll have a good think about what i really want from both boat and engine and hopefully get started very soon. Once i make some headway i'll be back to pick your brains again.