51 inch Mystic Style Mono Build

[Andrewc]

I finally purchased this 51 inch Mystic style mono hull from a company in China as a 50th birthday present yo myself. I have no idea why as I have no clue as to what I am doing, but it is enjoyable.

It is a fibre glass hull which I have strengthened throughout with carbon fibre and a 4mm marine ply strengthener to the transom. I have also added a bulkhead toward the front behind which I added floatation in the likely event I should crash it.DSC03767.JPGDSC03806.JPGDSC03794.JPGDSC03805.JPGDSC03808.JPG

Really struggling to get these pictures attached properly but hope this gives people an idea as to what I am doing.

I have purchased:

2 x Leopard 5692 1090Kv Motors

2 x Hifei 200amp HV Esc

2 x Contra Rotating prop shafts

2 x Trim tabs

2 x Turn Fins

2 x Stingers

1 x Rudder

I am about to start positioning the hard ware to the transom and need some advice:

How far below the keel should the rudder project?

Should the stingers be as close together as possible or as far apart as possible?

Should the props spin inwards or outwards?

Where on the length of the boat should I aim to have the centre of gravity?

Hope someone can help!!!!

Cheers

Craigen

[Rocstar]

The stingers should be mounted as low and close together as your largest set of props will allow. Spinning the props out will be best for handling.

[Andrewc]

Thank you.

[Andrewc]

Hello again. I have the motors mounted at 100mm centres between the shafts. Am I best setting the stingers at the same centres so the flexis are bending less or should I go with 80mm centres which will be adequate for the biggest props I am considering?

Anyone any thoughts on how deep below the hull I should set the rudder?

ThanksDSC03820.JPGDSC03821.JPGDSC03829.JPGDSC03830.JPGDSC03831.JPG

[Andrewc]

Hello again. I have the motors mounted with the shafts at 100mm centres. I can place the stingers at 100mm centres to suit motors reducing the bend in the flexi drives or I can set the stingers at 80mm centres which will be ample for the biggest props I will look to use. Joel suggests the stingers be as close together as possible as do others. My question is am I best going at 100mm or 80mm apart giving the advantage of less flexi bend?

Anyone any thoughts on how deep the rudder should be set below the bottom of the hull?DSC03820.JPGDSC03821.JPGDSC03829.JPGDSC03830.JPGDSC03831.JPG

[Rocstar]

You will need to get the stingers closer together for any chance of getting the hull up on top of the water. You won't be able to spin wheels that big anyway. Here is a 59" mono I built. There are some pictures of the rudder and stinger setup.

http://forums.offshoreelectrics.com/...uot&highlight=

[Andrewc]

Hi Joel. I have studied this build on another forum and have already taken a lot of ideas from it, so many thanks. Looks a superb boat. The water pick ups are obviously flush on the base of the hull so why when you buy them are they a "small square" on a large square if you get what I mean. If I install mine flush with the bottom of the hull I will have a small channel running round it. Am I not getting it or do you just fill this? Cheers

[Rocstar]

Only cut out your hole to fit the "small square". The step is suppose to sit on the inside of the hull, but depending on how thick the layup is you may have to modify the area where they sit. If this makes sense.....

[Andrewc]

Makes sense thanks. How much above the bottom of the hull should the flat surface of the water intake be? I am taking your advice regarding stinger centres and will move them closer together. I can actually move them to say 70mm apart. Obviously the more I move them in the more the bend on the shaft. What say you. stick at 80mm centres or go to 70mm and risk the tighter bend? What centers are you stingers at?

Many thanks

Craigen

[Rocstar]

How much above the bottom of the hull should the flat surface of the water intake be?

I'm not sure I follow. They should be flush with the bottom of the hull.

I am taking your advice regarding stinger centres and will move them closer together. I can actually move them to say 70mm apart. Obviously the more I move them in the more the bend on the shaft. What say you. stick at 80mm centres or go to 70mm and risk the tighter bend? What centers are you stingers at?

If it were me, I would get my motors closer together or separate the mounts and angle them. Otherwise you will have to make S bends to get your shafts to line up. I designed my own mount for this reason. I think my shafts were 67mm on center which is as close together as the motors would sit, plus I only planned on running props no larger then 60mm. MBP also makes a nice carbon fiber twin mount that would work.

http://mbp-rc.de/navi.php?suchausdruck=twin+56&JTLSHOP=e7469e0e013e7e9ce6c6ffbb39d50853

I'm not familiar with your hull, but IMO you really need to get the stingers as low as possible or the hull will most likely run wet. Think about where you would mount the stinger if it were a single compared to twins at 80 or 100mm apart....

[Andrewc]

Hi Joel

Hi I have installed the stingers at 70mm centres and they are as low as possible. The brass shafts are about 1mm above the bottom of the hull. Pictures attached.

I have adjusted the holes for the water inlets so the base of the water inlet is now flush. Is that correct? I haven´t glued them in yet.

Another problem, sorry opportunity (!!!) is the rudder v Stingers. The rudder is 150mm from the transom to the front of the blade and then the blade is 30mm wide. The stingers at full length have the props hitting the blade so I have to reduce them down to 115mm and then the prop, dog drive and nut make the total length up to 149mm so I have 1mm of play or more if I reduce the stinger length. Will this be okay, or do I need the rudder further from the transom?

I can have the existing motor mounts milled down so the centres would be 80mm the S bend would then be minimal (5mm per shaft) as opposed to 10mm. I´m not worried about making the bends, but how much better will the performance be if I can get them virtually straight?DSC03839.JPGDSC03841.JPGDSC03843.JPGDSC03844.JPG

Thank you for all your help as there is nobody in Spain who seems to be into fast electric boats so it is proving rather difficult and lonesome.

Thanks.

[Rocstar]

Looks good. I like to try and keep my flex shafts as in the straightest most direct route possible. Whatever you can realistically do to minimize the bend. If you're comfortable with an S bend, go for it. I would shorten your stingers a bit more if possible or make a standoff to extend your rudder and give yourself a little more clearance.

Not too many people in the States building larger twin monos either....

[MarkF]

I alway wondered why people think S bends are bad. There was a video around some time ago showing that a strait cable vibrating at speed and a slight S bend not. Personally I have always done what the boat wanted to get the shaft to the strut. I have more S bends than not. Besides at the power levels we have now do you really think your loosing speed one way or the other?

Mark

[Rocstar]

I alway wondered why people think S bends are bad. There was a video around some time ago showing that a strait cable vibrating at speed and a slight S bend not. Personally I have always done what the boat wanted to get the shaft to the strut. I have more S bends than not. Besides at the power levels we have now do you really think your loosing speed one way or the other?

Mark

I've seen that video also. I'm not opposed to an S bend, I've had to use them before myself. But if you can set it up for a more direct route (especially with 1/4'' flex shafts), why not? And I don't think it's a matter of "loosing speed" as it is wear on a flex over time.

[MarkF]

In over 20 years of doing boats I have never wore out a drive that wasn't related to where it goes into the collet or from rust. Tunnel hulls are a different story with there massive bends.
I had a sport hydro that had a very strait shot and it would vibrate like crazy on the bench when you spun it up. On my next build I put a slight S bend and it was smooth as can be. That was over 15 years ago and I never worried about S bends again. I only brought this up because I thought it was crazy for Joel to mill out his motor mounts just to avoid an S bend.

Mark