chris.-.

ok i had a nitro hammer and it was cool and all but i thought i would build my own boat for the fun and race it now i live in australia so i race it at penrith regatta centre when im done building. right now i have a hull that is a 40 inch cat i want to make it wickedly fast so im putting a 1.01 sized cmb rs hydro/offshore engine in it i am going to do a dual rudder set up on the left and right of the surface drive prop i am not sure of the size or pitch of the prop i need but i am sure there is some formula to find it could some one please help me by giving ideas on how to do a surface drive on a cat and the duel rudder setup i am new to baots but have been reading up alot i know an easy way to do it with the rudder but not sure of the prop as i do not know what sized shaft i need i am in no hurry im not going to actually start buolding for another few weeks i just need your ideas and help also ide like to no what szed trim tabs ill need and will i need turn fins also should i go with a 1.5 litr fuel tank or bigger ? or even smaller? my nitro hammer is fun but too slow for what i like i liek alot of speed i want to try to reach 100 mph but im not sure if its possibly with the size of my hull if not maximum hull speed would be nice

all ideas would be nice even if its not on things ive asked for as i am new and need to do more research before i cut and drill my hull im only a first year aprentice and will be bying things over time ie engine 1 week and maybe a month later a few other things it is a project for me n my dad to build but because its my hobby i have to pay for it if you want some pictures of it i will put them up also if u want pictures of my nitro hammer i can put that up too sorry for the long post but all help would be nice oh and sorry about the bad spelling if there is any i wrote this in a hurry and im used to msn and txting

piper_chuck

My Feedback: (12)

Welcome to RCU.

A dual rudder setup is overkill and just adds drag. Use a 1/4 inch shaft for that size engine. Depending on the cat, you shouldn't need trim tabs. As far as speed goes, it's unlikely you will reach 100mph with a cat. It takes a very precise setup to reach that speed even with an outrigger. Perhaps it's possible, but it's very unlikely...

ryan_t888

IMO going from a 20mph to even an 80mph boat is much too large of a jump. A 45mph boat will keep you on your heals. I don't think your cat hull will reach even 90mph. As Piper said, even a rigger can be a decent challenge to exceed 100mph. Very few do it.

I'd use a tank around 20+oz for that size engine. Also a Prather 265 would be a good start.

Ryan

chris.-.

well i have had a go of a few other peoples boats that go fast so its not that big of a jump i was told that it would be hard to stear if i didnt use dual rudder and that a1.01 sized nitro engine is too big but i want the power and besides that trim tabs should make it a little more stable i was told this by thye owner of the x cell hobby shop here

chris.-.

also i forgot to add im a toolmake aprentice i can make custom parts and engine mods to work the engine very easily i have a few ppl at the shop that do it to there nova rossi car engines so i cab get help there this hull probly wont reach 100 mph which was my mistake we work in kilometres over her i thought they were the same i did a little more research 100 mph is 160 kph i meant ide like to reach 100kph as a goal

piper_chuck

My Feedback: (12)

I did check when I replied, you did say "mph". Anyway, now that we're on the metric system, your goal of 100 (kph) is attainable. For reference, I've got a 36" Aeromarine Sprintcat. I've run it with an OPS .67 and an OS .81. The specs on the boat say it's made for a .45 to .80 size engine. It ran great with the OPS. It also runs great with the OS, but to be honest, it's a bit too much power. The only reason I switched from the OPS to the OS is that the OPS threw the rod and in the process broke the piston and bend the liner. I spent less on the almost new OS than the replacement parts for the OPS would have cost me. In racing conditions I need to be more careful with the .81 than I was with the .67, there are situations where full throttle will result in a "did not finish". I've never measured the speed, but I know it's fast. It has a single rudder and that's enough to allow it to hug the bouys at full throttle. It does not have trim tabs.

So, a CMB 1.01 is probably going to be too much for a 40" cat. You're going to end up with something that will be fast in ideal conditions, but a pain in the butt when things are less than ideal. If you haven't already bought the engine, consider a .67 or .80 rather than the 1.01. They'll both give you enough horsepower, but not have so much that some is wasted.

chris.-.

ok cool the places where i run it for fun is not where i race it they are semi inclosed and are ideal all times even after heavy rain as the most ive seen the chop there only be 2 to 3 inches and that is just after a storm ide like to know exactly what speed it kilometres is attainable for this hull it only cost me 100 aussie because i got it off my dads mate who has the moulds i havent got the engine yet but ide like to go big because when i do use it i like to slow down to a safe cornering speed and do tight corners then floor it down straights i have played with rc cars since i was 4 im 16 now they have all been cheapo k mart ones altho i like to modify them with hobby bateries i have no working ones left coz the battery killed them the nitro hammer i have modified i put a scoop over the carby and i reduced the compression by running with 2 washers in where the glow plug goes rather than taking out shims i have it runing at maximum stable hull speed and i am only using 16% nitro i can use 20 for more power but it probly wont give me more speed also i know this isnt to do with boats but i ordered a rider heli which is the air hogs havoc heli and i made a little search light for the front i havent tested it because it hasnt came yet it only wieghs 16 to 20 grams i weighed it on my mums kitchen scales will this helicopter actually be able to pick it up if i attatch it ? also why wont i need trim tabs my nitro hammer needs them?