MrMikeG

Correction noted Dave, how much does the angle of FSRV drives effect your torque though? The reason I ask is some US Cracker Boxes run submerged drives but parrallel to the bottom without tabs and have no noticable torque roll.

DaveMarles

I think Crackers are not what I called submerged drive. Parallel drive can improve fractionally the torque problems on fully submerged drive boats but torque is still the major problem. For example apart from all the built in hull correction my zenoah FSRV boat also needs 800 grams of weight on the left side and thats using a prop of only 59mm diameter.

patriktegelberg

Mike, about the theory and running boats difference. I get a feeling I am deemed a "keyboard boater" in your eyes, granted I do not have the amount of experience you have. You may be bothered by keyboard boaters but do you know what bothers me just as much? I am bothered by big shot wanna be boaters that have seen lots of boats but in reality have not understand what they have been looking at. You are most likely just missunderstanding me and understand it all, but so far your post look pretty skewed.

Dave, sorry for not coming through clearly. I will attempt to sort it. I differ between the concepts of walk and torque. This is about torque. Also I am not advocating the "no turning/zero rudder deflection".

In the side to side direction when running straight with a surface drive there are two forces acting on the transom. The propeller force striving to the left and the rudder force striving to the right. The rudder force is due to the rudder deflecting water. (Flabum) This will not create dog-tracking if the rudder has the right stand off. The two forces act on different heights thus creating a torque to counter the prop torque.

In a coordinate system where X is along the keel and Z pointing upwards. The rudder (obs) torque can be described as Frudder * Zrudderforcecenter + Fprop * Zpropshaft. If Z-origin is taken to be propshaft center the torque becomes just Frudder * Zrudderforcecenter in the counter direction of prop torque. So that Zrudderforcecenter is proportional to rudder length and the right lentgh will balance the prop torque.

Really hope for you to get this enough to argue against or with me.

DaveMarles

Patrik you do Mike G a disservice. Like all of us, I'm sure he doesnt understand everything but he knows plenty about boats and has an open mind to listen to others ideas. Keyboard knowledge is interesting but results derived from empirical observation are what matters when we are actually running a boat even if the theories we derive from those observations are flawed. Having said that its interesting to follow your calculations to possibly see a way of improving the running of my boats.

Regarding the forces. As I see it ...
Because of torque the propeller is pushing the transom to the left but this is making the boat want to turn right. The rudder water deflection is dragging on the right side of the boat and this is also making the boat want to turn right. The 2 forces are not opposing each other but rather they are complementing each other.

patriktegelberg

My appologies, I have seen that Mike is a very experienced boater. But he is not particularily open to learn from my posts and have quite frankly been a bit condescending.

glennb2006

Well then do wedges work on surface drives?

I imagine correctly designed and positioned wedge would counter the "rolling" forces on the hull from both the propellor torque reaction and rudder drag, and be a useful way to improve hull trim?

Glenn

DaveMarles

Patrik, I guess not everyone is too happy about theorists coming into the hobby and telling us that we know nothing or we are doing it all wrong. I'm not saying that it applies to you but it has applied in some cases.

Anyway I prefer to discuss boats..

Glenn, Torque wedges on monos may or may not work, I've not tried them or seen them used but personally I think the main issue here is propwalk not torque roll. Monos with surface drive do not exhibit what I call torque roll in any significant way although one would think that they would. Propwalk can be reduced as has been said before by sharpening the prop correctly etc. Offsetting the shaft slightly to right of centre will enable the boat to track straight with no rudder offset which is very important but the hull can still lean over to the right and in fact this leaning tendency can become worse after offsetting the strut. I've tried angling the strut to the left with shims/washers under the right strut bracket but thats not worked for me. The hull lean can be removed completely but I wonder if others have found out how to do it. I saw this written about years ago by Ron Franks and I followed his ideas and some of the ideas of John Finch in trimming out my monos and now I'm able to run without trim tabs and without torque wedges and have an easy to drive boat and little if any hull leaning. In fact on my .45 nitro mono I managed to trim it so that when jumping waves it corrects to the left and doesnt roll to the right. This is not perfect but was possible without trim wedges or trim tabs. Of course, immediately the prop size or type is changed, the boat must be retrimmed but thats normal for any boat.

glennb2006

Thanks Dave.

Clearly the amount of time you have run boats has given you a massive amount of experience, which is priceless. I appreciate you sharing it. Interesting that a mono can be trimmed without the additional drag of either trim tabs or wedges.

Now I have the challenge of finding out how to do it!! Off to google "Books by Ron Franks and John Finch"

I am thinking there may be a market for a book "trimming and operating fast RC boats" by D.Marles.

Ever thought about it?


Glenn

DaveMarles

Glenn, The Ron Franks info I got from a forum reply a few years ago on Jims Boat Dock. John Finch wrote a great article or series of articles in the IMPBA Roostertail December 97 issue called mono mania but as far as I can see its not around although someone on International Waters forum might know where it is.

martno1fan

Glenn i think John Finch wrote a book on the subject but i could be wrong.,it may have been a series of articles.Patrik dont be detered by peoples remarks or attitudes keep up your research and experiments .heres an article i read today.
[link]http://rcboat.com/jantech.htm[/link]

patriktegelberg

Mike, to you I apologize for not agreeing with you. You are no doubt a better boater than me and I would have wanted to learn from your experience. The “this is how it is and that’s that” was just not really up my alley.

I may have nowhere near the experience of the pro’s here but I have raced some, built ten boats seven sets of hardware and two molds. Not much but enough to get beyond keyboard status I had hoped.

This, I have figured, is just not the forum to express my thinking in. I started this thread to present from the theoretical point of view how one aspect of the boat works. Without telling anybody they were wrong. Did not go over to well.

Stay in the box and do not rock the boat. Yes sir, will do.

martno1fan

now you know how it feels pat,while i too am not experienced in setting up gas boats or building hardware or electrics im not a fool and i am a time served boat builder and have built boats from small tenders in wood to larger wooden craft and have fitted out large luxury yachts upto 120 ft long so when it comes to building i know which end of a boat is which.yet ive been treated like a fool on this forum by far too many so called experts.do not desert us mate i for one like your humour and you querky ways.your one of the good guys on here and but for people like you i would have deserted the site yesterday and almost did but by popular demand IM BACK hehe!!.

DaveMarles

Patrik, maybe there is something lost in translation because I would not like you to disappear from the forum and I'm sure Mike G would not want that either. Of course I can't speak for him, but he is Australian, and so we must make allowances for him. [>:]
Whether he is a better boater than you or I, I have no idea but thats irrelevant.

Can't we get back to discussing boating again?

Mart, Your signature, its the wrong way around. Chill out.

glennb2006

I found the book on Amazon by John French. Advanced R/C Boat Modeling . So I bought it. Will let you know what it is like when it lands.

Can't find anything so far from Ron Franks, will look some more.

Thanks for the tip on the author.

Yes I agree, back to boats and emotions in the boxes on the shelves where they belong.

Glenn.

patriktegelberg

I really hope I did not come across as making a childich threat of leaving. I will keep
going as usual. Use and develop the theory and read and learn from others. I will
probably not try very hard to learn others how it works though.

I do not know it all and could learn alot but not from "believe me" attitudes. The "everybody says this so it is right" deters me.

I am all here to talk boats and not to whine. My language is not (theoretics not Swedish) working to good though. Some do not want understand it, or ever hear it. This is Newtonian mechanics and if I can not get you who have a PHD in mechanics and are arguable the most experienced boater to see what I am saying, then I loose confidence in how I am perceived.

I like this passage as quoted from you:

"Offsetting the shaft slightly to right of centre will enable the boat to track straight with no rudder offset which is very important but the hull can still lean over to the right and in fact this leaning tendency can become worse after offsetting the strut."

I have not tried that this is true, only the most perceptive boater would notice, it is exactly what I am talking about and would have predicted if asked. I see this alot that you have really tried what happens and drawn the right conclusions, others not so much always.

If some one is selling knowledge I am sure to buy, but I am a tough customer. (And perhaps bad salesman)

DaveMarles

Too many fragile egos on here.

Firstly I don't think the monomania article is around now. I have a copy I printed off when it was available. If someone in UK is willing to type it into a word or .pub file I'll send it to them and they can give me the file and I'll put it up on my website. Its about 4 A4 pages long .

Back to boats,
Patrik, By extension would you say that if I have a boat with close to perfect equilibrium and no leaning to the right that if I shortened the rudder then the boat will lean to the right ? Its not a trap. I'm willing to do an empirical test on my .45 boat to check it out.

patriktegelberg

Yes, that I am saying but it could be hard to percept or possibly obscured by secondary effects. How long are the rudders now and how short do you expect to get them. With double rudders shorter rudders are possible with retained stering and walk resilience. Some boats ago I run really short double rudders and noticed the right lean, so I am not all theoretical, it was such things that started me thinking about it. If you could test not only the diff normal to short rudder but the diff to long to to short rudder I predict there to be a perceivable difference.

I guess I would be as hard to convince by contradictory tests as others are to be convinved by theory. So if the test came out negative you would have convinced everybody here that I am dead wrong except me. To convince me you only have to explain in theory why I am wrong.

But yes, it is what I am saying.

patriktegelberg

Make it without turn fin.

glennb2006

Firstly I don't think the monomania article is around now. I have a copy I printed off when it was available. If someone in UK is willing to type it into a word or .pub file I'll send it to them and they can give me the file and I'll put it up on my website. Its about 4 A4 pages long

I sent you a mail with my fax umber on Dave, fax them to me and I will type up and return for posting.

martno1fan

glad i could help on that book glenn my mate rick has the same one and its good reading according to him.by the way pat ask rick about the tests he and a guy at college have been doing in test tanks regarding prop walk etc.
Dave im chilled mate ,allways as you know by the way no one makes allowances for us yorkshire lads so why should the ausies get preferential treatment .

DaveMarles

Patrik, Turn fin should be irelevant as it doesnt touch the water when going straight. I still do not understand your reasoning. When you make the rudder deeper it will have more drag which will surely be trying to make the boat lean to the right some more.

DaveMarles

Martin you are a bit thin skinned for a Yorkshire lad, been in Blackpool too long?

patriktegelberg

It will touch when it leans right OK if in air off course.

OK since I am confident you are able to understand this I will try again.
I will work on it a while but in the meantime we could try to figure out why there is much more torque with submerged drive than surface drive. To me if one got that the other must follow.

patriktegelberg

I have drawn two pictures and scanned. Hopefully they are readable. I will just post them and probe how much they speak for themselves.

johnnyx

Would the width of the rudder from leading edge to trailing edge not affect this, the wider the rudder the more surface area in the water ?