tt-r

Hey all.
I have read a little about turnfins on the vintage hydroplanes, and understand they where from the 50's and on mounted on the inside of the left sponson to gain from the lift it will produce in turns. Of course on a modelboat the fin would have to sit on the right hand side. But my question is will this work on a model boat? Has anyone here tried it in real life? It would be nice to ad a scale turn fin to a otherwise scale boat.

I Just cant help but wonder if it's a negative effect to have lift on the inside sponson in a turn, not to mention the drag it will produce with all that water in contact with the hull.
i added some pics to show what i am talking about.

Thoughts anyone?

martno1fan

Never heard of a turn fin creating lift in the turn theyre suposed to plant the sponson in the turn,if you turn the oposite way then sure it will create lift.I run the zippkits turn fin on my rockett which is a bent fin so yes if i turn hard left the sponson lifts however in a right turn she turns awesome even at full speed with no signs of any lift caused by the fin.I dont see any reason why you cant use a fin similar to the one in your pic though.Why not try it and see .
Mart

tt-r

Thanks for your reply.

The lift im concerned about are the masses of water flowing upwards on the inside of the turnfin when turning hard right. On your zippkit boat the turnfin are mounted on a bracket at the sponson transom. When you hit the right tuns hard, you will see loads of water spraying up from the fin into the air. What do you think happens if this water hits the flat surface on the inside of the sponson instead of spraying out in free air?

Im not saying youre wrong, i just wish to know what people have experience with on theyre boats.

martno1fan

As you say it is on the transom on most if not all of the model ones.That said if you put one on the inside edge of the sponson the water rising up the inside of the fin as it turns will be hitting the bottom of the tub not the ride surface so id say it wouldnt cause too much if any lift.I say give it a go it would be worth trying because if it works mounting fins would become a lot easier and no need for a bracket either.If you do try it keep me posted id be very interested to see how it works.I might try one on my own design the Comet cheers.
Mart
heres my zippkits running flat out in the turns 60+ mph
[link]http://www.youtube.com/watch?v=wVGBWC_3MuY&feature=channel_page[/link]

tt-r

Youre right about the water hitting the tunnel inside and not the ridesurface. And maybe its not a big problem with lift after all. But they altso talk a lot about drag when water from the fin hitting any part of the boat. It will be a while before i have the possibility to try it out myself. These days im vaiting for the supplier to restock the zippkits before i can place my order. So i encourage you to try it out since your boat is up and running

Very nice running boat by the way. Thanks for the video mate.

martno1fan

Thanks mate the red one i posted the pic of has similaritys to the rockett as i used the same angles on the sponsons and the ridepads are the same as the ones for the zipps.Mines 50" long so a bit bigger and obviously glass but they run well the first one i sold is running at over 50 with a stock rcmk in it.Hope to test the red one myself with the same motor as in the zipp which is a fully modded ss zenoah.if your ever interested in a glass t boat keep me in mind .I might try your idea on the red one,im not changing anything on the zipp apart from ill be installing new ride pads to get her even faster.
Mart

Hydro Junkie

Hate to say it Mart, but water hitting the bottom of the boat can flip the boat. A friend tried to race a Dumas Atlas with the skid fin mounted on the inside of the sponson. His boat spent more time upside down than it did running. He found that between the boats slightly narrow tunnel and the skid fin water hitting the bottom, the boat would roll almost at will. He ended up widening the boat and moved the skid fin to the sponson transom. After he made those two changes, the boat would hold a full throttle corner. With the Wildroot Charlie, it's not fast enough to make a difference with a G230 for power. The reason I can say that about the Charlie is I've worked on and driven it. The picture was taken at the Hydroplane and Raceboat Museum in Kent Washington where the 60 inch long boat is on display. Here's some more pictures of it

martno1fan

You could be right mate but as regards the dumas boats a friend over here has one,been a true scale t boat it just does not handle well at all.The zipp isnt true scale nor is mine ,has a wider tunnel and the sponsons are much bigger than the scale ones at least the one ive seen anyways which is probably why they run very well as a model.I still think ill maybe give this fin under the sponson on the inside edge a go,def nothing to lose.Nice boat in the pics.
Mart

dicko

Having the turn fin mounted on the inside of the sponson only works on riggers as there is nothing for the water shooting up to hit. On a sport hydro or thunderboat it will hit the underside of the sponson wing & create unwanted lift in the corner resulting in a bad handling boat as Hydro Junkie said. It has been tried & it doesn't work.

martno1fan

Well when turning the water is forced up the inside edge of the fin so it shouldnt hit the sponsons at all,the only place it will hit is the bottom of the main hull which will be out of the water so any water hitting that should either run back or up the non trip sides so i think it might just work.I wonder how many have actually tried it to be honest.I could be worng and it may still cause too much lift but i think i might just give one a go and see.
Mart

tt-r

Im happy to hear about real life tests with this setup. In theory this is not an ideal setup, and it sounds like the people that tried it didnt get good results. But please Mart, keep me posted if you decide to give it a go.
Thanks a bunch for the pics HJ, that really is a beauty. Incredible details, i just suspect that the pics dont do the boat justice. I wish i could see it in real life.

tt-r

By the way, how scale is the Zippkit Rivett anyways? Is it possible to get a more or less scale apperance or is the shape on these kits too odd? Ive never seen one in real life but am going to get one anyways i think.

martno1fan

They arent true scale but they do look scale enough if you get me and can be made to look very real so yes.Theyre designed for performance and boy do they perform.The cowl is a bit over sized for my liking ,the main reason i made my own for the comet more in scale with the rest of the boat by keeping it lower.Heres a cpl of pics of some rockets the green ones mine,also notice the scale dumas slomo shun which by the owners admision is not the best runner .When i designed my Comet i asked Joe if i could use the same sponson design as i knew how well it worked .Ones bigger than the other the ride surface is 1/4" wider on the left sponson which allows for great turning without losing straightline speed or stability and they run stright as an arrow.Checkout my pics of the Comet on the website bellow.
Mart

Hydro Junkie

Okay Mart, let me see if I can clear this up for you. The water from the turn fin doesn't hit the sponsons, it hits the boat bottom. Due to the speed of most boats, the force of the water hitting the bottom is enough to lift the boat. A majority of the full sized boats have only 12" from sponson bottom to hull botton. On a scale boat, that equates to 1.5", so the force of the water doesn't have a chance to disipate before hitting the bottom. This is why the full sized boats moved the skid fins to the back of the left sponson back in the early 1970's. The results were a dramatic increase in lap speeds. this one minor change allowed the boats to go from around 95-100 MPH per lap to 120+ in 1973, which was when the brand new Pay N' Pak and the former Pak, now a Budweiser, both ran over 120 MPH in a then record setting heat with the Pak winning by less than half a boat length. By looking at this picture, you can see how much water is coming off the skid fins, more than enough to roll either of these two boats

martno1fan

Well we shall see if its works or not as im going to try it anyway .plenty said i wouldnt get 65 mph from the zipp but i did in fact ill get 70 .I dont get near that amount of water rising up my turn fin as the ones in that pic,in fact none when running straight that you would notice.
Mart
[link]http://www.youtube.com/watch?v=_uvOdbGNkcM[/link]

[link]http://www.youtube.com/watch?v=wVGBWC_3MuY&feature=channel_page[/link]

Hydro Junkie

But Mart, those boats are in a 50 foot radiused turn doing over 50MPH. On the straights, you don't see any water coming off the skid fins since there is no side loading going on. The side load is what creates the spray coming off the skid fin

tt-r

Great input HJ, thanks.

Mart; brave of you to decide to try it out no matter what. The worst thing that would happen is gaining experience. If its worth it when people with experience says it wont work can be discussed. But best of luck I would like to hear about the results.

About the massive waterspray from the turnfins in hard cornering, thats one of the main reason i think thunderboats are so facinating. A full scale race with a pack of boats rounding a corner. Just a big wall of water behind them. I think thats an awsome sight

martno1fan

Yea im aware of that mate,mine turns at full tilt too but i still dont see that amount of water coming up off the fin as in that pic mind you im busy driving and dont have the benefit of a still pic to study so i could be wrong.Its all good mate were just discussing and its good to have your knowledge of the real boats to work off even if i do ignore it and say dam it im gonna do it anyway .Im sure you are probably right im just stubborn and like to find things out for myself,ill be the first to say you were right if it doesnt work.TT-r not sure what your name is ? but till you have run one you wont understand what a thrill it is to drive one .
Mart

jacob711

i can remember some talk of hydro turn fins, apparently even having the fin on the outside of the bracket can be bad as the water coming up hits the bracket it causes lift

martno1fan

Thats what it says in the zippkits manual but that said ive seen plenty run them with the fin on the outside of the bracket and they havent had any problems so not sure if thats the case.
Mart

dicko

The bottom of the bracket on my whiplash has been rounded to reduce the lift effect because it is mounted on the outside. if it were square it would cause too much lift in the turn. on my FE rigger the fin is mounted on the inside of the bracket so that it doesn't flip in turns, I had it the other way & handled terribly, once I put the fin on the inside it turns on rails.

Here's a pic of my whip so that you can see the rounded base of the bracket.

Hydro Junkie

I can see where the water hitting the bottom of the bracket could cause problems in a rigger. On a scale style hull, I have never seen it as an issue. No worries Mart, I can understand since I've been there myself. Nothing I like better than a friendly debate or discussion. That all changes when someone starts attacking another person because they disagree with someone's opinion. I don't see this happening so no worries

martno1fan

Never in danger of that mate,i respect your advise and your knowledge.Im not disagreeing with you at all as i said you are probably right.I probably wont get to test the fin till the back end of the year anyway as im too busy building boats right now.
Mart

tt-r

Since we all are talking turn fins here, i have one more question. What is the main reason the turn fins often are bent or curved? Is it becouse of the g-forces bending the fin during tuns or is it for having more grip in turns? Like the wheel angles on a car perhaps? It certainly sounds right to have it bent for better grip, but i have read somewhere about the fins bending a lot in turns.

martno1fan

I believe the hooked fins help keep the boat hooked into the turn,that said lots of guys run fins with no bends.I like how the zippkits one works as it seems to hold her steady in the turn even at full speed.It can also be moddified to help reduce drag but i havent done that yet either.So far i havent tried any other fins but as i said before that will change on the comet ,as soon as ive finnished the one im building for a customer ill get to it.
Mart