DF Sniper 45 T-Mono Build Target 100mph

[properchopper]

Tyler, Far be it for me to offer advice on such an ambitious build, but after seeing and experiencing the ravages of those pesky high speed SAW dances, something disturbs me about the picture of that looong rudder mounted on the back. Lots of lateral leverage there relative to the dimensions of the mounting foot, when or if things go awry. Bracing struts could help prevent undue forces from ( I can't even say it) but you know what I mean

[RaceMechaniX]

Hey Tony,

The bracket is pretty beefy, but I do expect to be bending rudders. This one is still full length. Eventually I will cut it down to the best compromise.

Tyler

[properchopper]

Hey Tony,

The bracket is pretty beefy, but I do expect to be bending rudders. This one is still full length. Eventually I will cut it down to the best compromise.

Tyler

Tyler,

Agreed, the bracket IS ultra beefy and will not bend. As a result, what worries me is the rudder assembly being torn from the hull (shudder) from sideways forces should things go "incorrect" at max velocity. That's where some strut braces would come in handy. We both know what an Impish Devil that Legg Monster is

Consider the following Formula :

S = Mv x Al x 100P x mLM x (x)H/W

where :

Sr = sideways force on rudder assembly
Al = area of mounting foot relative to it's length
Mv = max velocity
P = probability of 100 mph cartwheel
mLM = mood of Legg Monster
(x)H/W = number of horses for wife to justify project

( I'll go back to my room now ; oh wait; I live in a one room apartment )

[RaceMechaniX]

T,

It's the last two variables that scares me the most.

TG

[thomaslambo]

The idea behind the flooded stuffing tube is to allow vertical moving of the strut. If you just had the stuffing tube pass through the transom and it was a tight fit so it sealed the water then it would be impossible to allow for any strut adjustment. In nitro and gas boats we just make an oval hole in the back and leave it open for water to drain out. In the FE boats, we have to seal it, so we install a larger tube which the stuffing tube fits in. We epoxy the tube in the rear on the OD to seal the tube to the transom. In the front of the tube, we seal the stuffing tube to the ID of the big tube. Now we have a sealed tube, but with th extra length between where the stuffing tube is sealed and where we have the strut we have enough bend allowance in the stuffing tube to make strut adjustments. The stuffing tube is supported near the motor by the expoxy and its supported at the rear by the strut.

Hopefully that all makes sense.

Hi Tyler,

I’ve been following this thread and my compliments on the quality of the build. I'm looking forward to seeing it run :)

I have a question regarding a Strut vs Stinger drive system. I really like the flooded stuffing tube design and how it allows vertical adjustment of the Strut.

I'm just getting started in FE boating and have spent most of my time with Mono’s that exclusively use Speedmaster Stinger drives. However, I have a couple of Cats as well that use Struts (for obvious hull design reasons with single motor setups) and these can be adjusted in a similar fashion due to the long length of stuffing tube outside the hull..

I'm in the process of building a "P" class SAWS boat and was debating whether or not to use a Stringer vs Strut drive with a similar system to yours (unless I go rear motor setup...which is another conversation all together).

So, my obvious question is; why did you choose a Strut drive over a Stringer drive in your boat…are there any performance considerations or is it just your preference?

Regards,

[Fluid]

While Tyler can certainly answer this himself, I will give my take. Mono stability at high speeds is critical. Some hulls work better than others, but it is always a balance between lift and keeping the boat stable in the water. Boat stability, particularly chine walk, is largely dependent on how much of the hull is in the water. Trying to balance a mono on the tip of the vee invites small outside fources - waves or a breeze - to upset the hull and initiate a side-to-side rocking = chine walk. The best and most positive way to control this, particularly with the large pitch props used in SAW - is to lower the hull into the water. Stingers only allow minor changes in prop height, and prop height is the main way to control the hull's depth in the water.

On the other side, if the hull is running too wet then raising it out of the water is needed if top speeds are desired. This requires lowering the prop to help lift the hull. A conventional strut allows this easily (with the flood chamber) while a stinger does not.

Bottom line - with the stinger you have to guess at the approximate vertical position of the prop. You have much more leeway with a strut. It is really a tuning aid that can mean the difference between a record and a crash....sometimes at least.


.

[thomaslambo]

Thanks so much for your reply Fluid.

I'm fairly new to this forum.....been reading threads for a few months now and bugging the heck out of Steve via e-mail.

FYI, I've seen many of your posts and benefited greatly from them

[RaceMechaniX]

Thomas,

Thanks for the compliments on the build. There are several advantages as pointed out by Jay. I choose the flooded design with motor upfront to allow the greatest flexibility for prop adjustment. As he mentioned, the set-up allows for both vertical movement and angular movement which key for tuneability. With a stinger you can adjust the prop height, but only with a corresponding angle adjustment as well. The strut allow for movement in both. Another reason I prefer the layout of having the motor in the front is it allows for the most direct and smoothest cable path. There is only a very slight bend which reduces the friction. At least in this hull with a big motor, if I had mounted the motor in the rear I would have a steeper angle to the stinger or strut. Consider that I am probably going to pushing 10kW+ through the driveline and every bit of friction reduction will keep the driveline healthy.

The set-up for SAW will vary greatly with different hulls, motors, etc so maximum tuneability is a key.

Tyler

[thomaslambo]

Thomas,

Thanks for the compliments on the build. There are several advantages as pointed out by Jay. I choose the flooded design with motor upfront to allow the greatest flexibility for prop adjustment. As he mentioned, the set-up allows for both vertical movement and angular movement which key for tuneability. With a stinger you can adjust the prop height, but only with a corresponding angle adjustment as well. The strut allow for movement in both. Another reason I prefer the layout of having the motor in the front is it allows for the most direct and smoothest cable path. There is only a very slight bend which reduces the friction. At least in this hull with a big motor, if I had mounted the motor in the rear I would have a steeper angle to the stinger or strut. Consider that I am probably going to pushing 10kW+ through the driveline and every bit of friction reduction will keep the driveline healthy.

The set-up for SAW will vary greatly with different hulls, motors, etc so maximum tuneability is a key.

Tyler

Thanks so much Tyler for the reply.

Regarding your flooding tube setup:

1 How do you support the Flooding tube at the motor end (e.g. cross brace like most stuffing tube setups or just with the flex shaft connection to the couple)?

2 On the other end, does your brass stuffing tube slide into the strut or just the nylon insert, the Speedmaster Strut I have (for the .187 flex cable with 3/16 shaft) is only large enough to slide the nylon insert into it, it will not allow the 9/32 brass tube to slide in (worried about support, or lack of)?

[RaceMechaniX]

The motor side of the tube is epoxied to seal the front end. The 5/16 tube slides all the way through the strut. I use a Speedmaster bushing in the rear. If you want to use a brass bushing in your set up you need to cut the teflon liner short and glue it in place or fasten it near the motor side so it will not slide back. Then you should have the length you need in the stinger to run a bushing.

Tyler

[thomaslambo]

The motor side of the tube is epoxied to seal the front end. The 5/16 tube slides all the way through the strut. I use a Speedmaster bushing in the rear. If you want to use a brass bushing in your set up you need to cut the teflon liner short and glue it in place or fasten it near the motor side so it will not slide back. Then you should have the length you need in the stinger to run a bushing.

Tyler

Thanks much

[z400]

Keep up the excellent work!

Boat is mean already!

[RaceMechaniX]

She is complete.

[RaceMechaniX]

A couple more pics.

[z400]

Super Sleek!!