Hi folks

My 47” Lynx Mono is fitted out with the traditional strut support. Am I right to think that this hull could be fitted with a stinger drive system (please bear in mind that I have no experience of using stinger drives)?

If so, are there any technical advantages or disadvantages with the stinger drive system (compared to what I have got)?

These two images hopefully show my set up. The stuffing tube runs parallel to the bottom of the hull towards the transom. Where it exits the transom the stuffing tube slides snugly into the housing of the CNC support bracket.

My concern with my existing set up is the limitation in the available angle of adjustment of the strut support. If I attempt to angle it down it is very limited by the end of the stuffing tube housed within the support. I am also concerned about having a relatively sharp bend in the flexi shaft (near the joint between the stuffing tube and strut support) even if the angle is altered by just a few degrees. Unless of course I was to remove the stuffing tube and attempt to put a gentle bend in it to suit the new angle, a job that would need some surgery. Current set up is with slight negative angle and strut as low as possible.

Does the stinger system allow for more adjustment or does the stuffing tube limit it in a similar way?

The main reason for my topic is that as I have increased the speed of my hull it now needs taming for stability in straight lines (purpoising and torque roll). Although I am going to try trim tabs, I feel that the best answer may sit within the drive set up.

Your comments and opinions will be much appreciated.

Cheers
Craig

IMO really ZERO difference in the way hull runs with either when prop position is equal.
Each type can place prop at same position behind transom, only the hardware used in doing so make the difference.
If there is a plus/minus of each ...
*Simplicity and compactness of the stinger type and ease of pulling cable when fitted with a flex ferule and square drive cable within a plug in cartridge unit.
* Conventional strut for easy adjustments and using basic multi application hardware.

Torque roll prevention requires VERY SHARP and THIN props. Pending hulls bottom profile ? ... tabs are generally required by most for a level running attitude.

In my honest opinion there is no real advantage to using a drive instead of a strut aside from the fact that it's easier to do fine-tune adjustments without losing your initial position.

What I would suggest is you modify the opening in the transom for the stuffing tube. Make it oval stretching it out to allow the strut to be moved up/down about 1/2" or so. That will allow good up/down adjustment and will also allow you to do slight angle adjustments without any drastic curves in the tube. I've done many this way.

Don't worry about water leakage into the hull. It keeps the hull low in the water if it dies...usually means less damage if it gets hit! If that really bothers you though, you can make a flexible seal around the stuffing tube with some silicone, or if you can find a suitable size rubber bellows that will work. I've never bothered with that though. Water might come in when boat is stopped, but when it's under power it bails out by that opening.

FTR, most monos I've owned liked the propshaft centerline at about 3/8 to 1/2" above the keel and mostly flat or with just a little bit of negative (propnut end down)on the strut.


Edit: OOPS... was a bit too slow, Scott beat me to it! He does have a good point about the square drive setup with the stinger drive... I hadn't thought of that... can you tell I use welded cables?

Hi Craig with torque roll as well as a sharp prop like Scott says i,ve also read to mount strut/prop slightly to right about 1/8" or less to counteract it.Daz

Hi Craig just looking at your picture of your strut and on that your strut angle looks bang on 0% but you,ve stated its slightly negative,it maybe the pic m8 unless your transom is also on a slight angle like mine.Been thinking about your torque roll problem & also i,ve read possibly moving weight to the opposite side of the boat which may or may not work,it,s all worth trying even adding some weight before moving things around first Craig!It,s all trial & error m8 so test test test like i have started to do m8.Cheers m8 DAZ

Mounting the strut/drive offset slightly to the right does help some if boat pulls to the right. That is a very good point that I forgot to mention. I do this on many of my boats also.

You have to keep in mind though that you get more propwalk when props aren't well sharpened and thinned and or boat is setup too loose. So you want to address these issues also, not just fix with plaster. Typically with a boat that's too loose you will also get chine walk, which means the boat bounces from side to side (chine to chine) when going straight. That's a good indication that it's running pretty loose. In a lot of cases playing with strut depth will fix this. There are a lot of factors that come into play when tuning boats! That's the fun of it all!

Does round ear propellers help reduce prop walk in monos?

Mercury94 wrote:
A props "Ear" profile is one addressing LIFT characteristics.
Tho that said a round ear profile having generally less lift will by that attribute alone tend to be less prone to inducing walk

Mono's generally tend to do best running lower pitch ratio props so prop lift is less overall . Then spin said prop at really high rpm

Hi folks

I didn’t quite expect to receive so many replies in the space of 24 hours. Thank you all very much for your very helpful and considered advice.

You’ve given me plenty to think about.

Just a few comments in response:
In view of the differences mentioned between the stinger and strut system, I will stick with my strut set up as I see little to gain in changing to a stinger.

My strut is offset to the right by about 5mm as per the build instructions.

However I do need a tiny bit of left rudder trim to keep the hull running straight. The strut is as low as it will go (I perhaps made the mistake of glassing in the end to make it waterproof). Next time I build a mono I will leave the oval transom gap open as suggested but make a little wooden surround or enclosure with a removable water proof lid. That way I can adjust strut height and keep the water out should the boat stop. Strut angle is close to parallel but very slightly negative.

Added bow weight is an option I considered but I will try the trim tabs (now installed) first.

The importance of sharp and thin blades of the prop to minimise torque roll is a point that really was delivered well.

It might explain why my boat torque rolls the least on my alloy X470 prop. This prop is one that I made razor sharp and weighs in at about 9 grams. It came sharpened but I made it a lot sharper. I expected it to disintegrate but it ran fine.

For my next run I have five props to compare again (all sharpened and balanced).
In order of boat speed for my stock Zen260PUM engine set up they are as follows:
Slowest hull speed first:

X470 2 blade Octura
X470 3 blade Octura
X472 2 blade Octura
X670 2 blade Octura
67/17 2 blade Mocom

The last 4 on the list all seem to deliver similar straight line speeds so there’s not much between them in that respect.

The higher pitch ratio of the last two props mentioned definitely suit my stock Zen engine, however those are the two that make the boat most scary. That fits in with what Scott said about mono hulls preferring lower pitch props with more revs.

Perhaps the greatest challenge for me about running Gas boats is that there is no perfect simple solution. For me that is what makes the thing so addictive!

Cheers
Craig

Craig,

Also let me add that in 20+ years racing monos both Nitro and Gas have universally found 3 blades to be smoother running than the 2 blades.

In recent years as our gas engines have been able to turn such good RPM numbers have actually dropped prop diameters to the 65/67mm diameters and pitch ratios in the 1.5 - 1.7 range. Doing so however places a lighter load on engine actually in a sense under propped. Have gotten around that by cupping up blades increasing efficiency a bunch while at the same time loading up engine more.

** Your right in there being no absolutes with many ways in getting to the same place ... SPEED !