jaycook

My Feedback: (1)

I'm planning to build a 70" hydro and wanted some feed back on the drive system here are my options:

1. MHZ Polini 50cc with, gearbox for twin couter rotating props.

2. MHZ Polini 50G which has a 1.42 gearbox attached to the motor. single prop.


which set-up would be better for acceleration and overall driveability? I'm not looking for the highest top speed I want good acceleration with a good top end, not looking for the fastest boat on the lake. with a boat this size I would be happy with 50-60 mph.

for drives, is it logical to use outdrives or should I use a strut system on a hydro? I like the outdrives but not sure if it would look "right" on a hydro even though they both are surface drive systems.

On a hydro this size is prop walk even an issue? I want it to turn the same (or close to it) in both directions?


Many thanks for your input!

Mr Cajun Gator

With a boat that size 50-60mph is a lot to expect. For the turning go with the counter rotating props, this will stop the prop walk and allow turning in both directions. It is a slower set up(twice the amount of water drag). For the drives surface has work well for me. Also on a hull that size you may want to look into steering servo set-ups. It may need to have two, 1/4 scale servo's on the rudder.

jaycook

My Feedback: (1)

thanks for the input, I definately plan to use 2 1/4 scale servos for the steering. the prop size will be a challange.

Hydro Junkie

Why go so big? People in Washington that have large scale boats stopped at 1/6th scale, or roughly 60"(more or less) Using B. H. Hanson G230 Indy's, they are getting into the 40+ range with a single prop on a hard shaft. I'm presently building a 61.75" 2003 Oh Boy! Oberto that will get either an Indy or full race G260, though I havent decided yet. I'm hoping to get 45+ with it, so I don't really expect you to see the speeds you're looking for with 50. I would also steer you away from a gear drive. In a hydro, low weight is a must and space is almost nonexistant. You also need to decide which way you want to turn it as well. To make a hydro turn, you will need to mount a skidfin on the back of one of the sponsons to keep the boat from just sliding sideways. Putting one on both might flip the boat in a hard turn, due to catching the outboard skidfin while turning.
If they posted, here are some pics of two of my boats under construction. One is a 1/6th scale 1973 Pay N' Pak, the other is a 1999 Miss Madison Turbine. The Pak is 57" long, the Madison is 46.5" long. On the Pak, notice how I've had to widen the engine bay just to make the G230 fit. I don't know what kind of hydro you're looking at, but if it's anything like these, you will be doing some serious modifying t get that engine in the boat

jaycook

My Feedback: (1)

Hydro Junkie,

Thanks for the input and the pictures. Isn't bigger better? just kidding.

I just wanted to build a large scale hydro. It's not much larger than the one you are building. I'm leaning towards using the MHZ 50cc Polini which weighs 8.5lbs is 10HP @16800 RPM. The gearbox is a MHZ with 33% increase in prop RPM to approx 22344 max and weighs 21oz. I figure with a hull this size two 2-1/2" props would push it better than a single 2-3/4" or 3" prop. I'm going to have custom struts and rudders, turnfin made at a local machine shop. I do alot of business with this shop the owner said he would make anything I needed.

I know a G260 can produce 5.3HP @ 16800 however it is only 25.4cc it can't produce the torque that a 50cc can. I'm looking for a fun boat to run not just top speed. I want it to have good acceleration and a good top end. I know it's hard to have both, I'm looking for a happy medium in each. If it runs 40 mph, I'll go back to the draing board to figure out what I can do to get a little more speed out of it. Prop selection will be key, if I can get 60%-70% prop efficiency then I should get close to the speeds I am looking for.

Hydro Junkie

Sounds like you have it all planned out. This is good to hear, as so many just decide they want a boat and jump in headfirst without a plan or a clue. Have you picked out a hull style/design yet? I would be looking at a picklefork, maybe a turbine style with the canards. Having less weight and being harder to blow over would make them my hull style of choise

jaycook

My Feedback: (1)

I have chosen a style, its a turbine of the miss budweiser. I bought a set of plans and templates. My plan is somewhat complete, I still need to figure out all of the controls and back up safety equipment like a remote kill switch. The hull has a 43" beam so it should be fairly stable. Before I start construction I plan to do some weight calcs based on the sizexs I need so that I can estimate weight and balance.

Thanks for your input, I will post pics as I go along and would certainly appreciate any possitive or constructive criticism. I'm sure I will run into stumbling blocks and may need input from others to get past.

thanks again, Jay

Hydro Junkie

It's not a plan set from Newton Marine is it? If so, there are some things I need to warn you about

jaycook

My Feedback: (1)

i bought them from an individual, not sure who made then but if is newton, i will let you know. thanks

wiz0852

My Feedback: (1)

Did you get them from Woodcutter4444, and if you did,how are they, I`m thinking about buying his last set... Gary