I really need specifics on chine-fins or "chicken wing" fins

[champ20B]

I need to know if transom mounted "chicken wing" fins were and/or are used on "B" stock and some 25SS "ROLL-UP" runabouts. I am specifying on roll-up types (that's what I have). If they were, what are the dimensions and are they in line with the bottom turn fin? Or are they more toward the center in relation on the transom or farther from?

Also, I would like to see a chine fin. THERE IS NOTHING ON THE NET SPECIFYING THIS STUFF. Does a chine fin protrude 90 degrees in relation to the chine surface? Or is it mounted on the chine but hanging 90 degrees in relation to the bottom planning surface of the boat? On which either, does it extend below, even, or above the waterline? by how much? and what dimensions?

I really need this information!! IT COULD SAVE MY HIDE!!!

On a side note, I'll bet more people would be likely to look into doing these kind of motorsports if VITAL set up info like this for one, was clearly explained, illustrated, and specified! I notice that when it comes to giving specifics as not to create unfair advantages, THERE IS PLENTY TO COVER THAT!......but when it comes to set up specifics that can save one from potential disaster, it as sort of SKETCHY!! I PREFER FEASABLE "OPTIONS" THAT IS CLEAR, COMPLETE AND STRAIGHT TO THE POINT. I would really appreciate this info from anyone who has experience that don't mind taking the time to post input for me and others in the future to see here on BRF. I know I do this at my own risk, Thanks!!

[Tim Weber]

Most guys did not and still do not use this type of fin.

The fins you are referring to were usually water ski size fins. Maybe 2-3 inches in length and 1 1/2" to 2" deep. When I have seen them on a boat they were usually placed on the chine as close to the rear and centered.

Craig Bowman of Brocolli Boats fame made some of his chines with a notch in them. It was roughly in the same position as a fin would have been.

Bottom line is if you have a well designed roll up, you don't need anything other than a fin on the bottom. A great, inexpensive roll up is a Trolian built Race Craft. There are bunches of them around and they are very easy to turn, at least I think so.

Tim

[Bill Van Steenwyk]

I need to know if transom mounted "chicken wing" fins were and/or are used on "B" stock and some 25SS "ROLL-UP" runabouts. I am specifying on roll-up types (that's what I have). If they were, what are the dimensions and are they in line with the bottom turn fin? Or are they more toward the center in relation on the transom or farther from?

Also, I would like to see a chine fin. THERE IS NOTHING ON THE NET SPECIFYING THIS STUFF. Does a chine fin protrude 90 degrees in relation to the chine surface? Or is it mounted on the chine but hanging 90 degrees in relation to the bottom planning surface of the boat? On which either, does it extend below, even, or above the waterline? by how much? and what dimensions?

I really need this information!! IT COULD SAVE MY HIDE!!!

On a side note, I'll bet more people would be likely to look into doing these kind of motorsports if VITAL set up info like this for one, was clearly explained, illustrated, and specified! I notice that when it comes to giving specifics as not to create unfair advantages, THERE IS PLENTY TO COVER THAT!......but when it comes to set up specifics that can save one from potential disaster, it as sort of SKETCHY!! I PREFER FEASABLE "OPTIONS" THAT IS CLEAR, COMPLETE AND STRAIGHT TO THE POINT. I would really appreciate this info from anyone who has experience that don't mind taking the time to post input for me and others in the future to see here on BRF. I know I do this at my own risk, Thanks!!


After having read some of your previous posts, the best advice I could give you (after a 40 year stint in race boats, both Hydro and limited in Runabouts) would be to calm down some. Lots of the things you are asking about can only be determined by testing, and testing some more, due to the both large and minute differences in race boats that have been mostly designed, especially for the last 30 years or so, by competitiors who race themselves. Consequently, due to their hard work in trial and error testing, they can be somewhat reticent to share with others what they have found out and made them successful.

The reason there are very few books or information of the type you are asking for is this is a minor sport, but one whose really serious participants
have learned what they know to be successful through much hard work, time and money spent, and are somewhat frugal in their desire to just give away what has taken them sometimes many years to learn. Also you do not have a large cadre of racing boat mfgrs who are building boats for sale and have financial reasons for their boats, (which might or might not be similar to yours), to be successful in competition and therefore have blueprints for modifications to achieve that success.

The several folks who are in this situation really do not frequent this site near as much as they are on Hydroracer. Not for any reason that HR is better than BRF, but BRF has found a home with many whose racing career is over and more past history is discussed than present build information.

All that being said, I can give you the following information regards a DeSilva type runabout that was built by Krier Boats of Ollie, Ia. I campaigned this boat in the RB class that probably ran at the time, 5-10 MPH faster than what you will achieve if you use the motor/motors you are speaking of. That boat and motor combo would run right at 70MPH and I won a National APBA Championship with it in 1986. I did use a small transom mounted fin ON the boat that was originally a sponson fin from one of my Hydro's. It did accomplish what I was looking for which was to cut down on the tendency of the boat to slide sideways so much in the corner, but it also cut my speed by a mile an hour or so. Almost everything you do when you put more things in the water causes drag, which will slow you down.

My advice, which I am sure would be seconded by most experienced boat racers, is before you get excited about what might happen when you have no prior knowledge of how the boat is going to perform in various water conditions is DO SOME TESTING. Try to attend some races in your local and talk to the racers, examine their equipment, and if they have time before or after the race, strike up a conversation with them and tell them what you are doing and what do they think about how it might work and what to stay away from. Since you are being somewhat mysterious about the design of you boat and no photos are being shown, it is very difficult to help you.

Again the best advice I could give you is relax, slow down, and test, for all the reasons I have described and more besides. Take some photos and post them of the boat running on the water and hopefully you will get some help you are asking for, and also try HR. I think for all the reasons previously mentioned you might get more help from present builders and racers there.

AND AGAIN, RELAX. Testing to first determine whether you have problems that need to be solved, is much easier on the disposition than wasting time and energy trying to figure out the worst that might happen, that is only in your mind and imagination. If you have a problem found thru testing, then you can spend the time asking for help solving it, or working it out for yourself. Then YOU are the one they will come to for the assistance based on the knowledge you have gained thru this build.

[champ20B]

After having read some of your previous posts, the best advice I could give you (after a 40 year stint in race boats, both Hydro and limited in Runabouts) would be to calm down some. Lots of the things you are asking about can only be determined by testing, and testing some more, due to the both large and minute differences in race boats that have been mostly designed, especially for the last 30 years or so, by competitiors who race themselves. Consequently, due to their hard work in trial and error testing, they can be somewhat reticent to share with others what they have found out and made them successful.

The reason there are very few books or information of the type you are asking for is this is a minor sport, but one whose really serious participants
have learned what they know to be successful through much hard work, time and money spent, and are somewhat frugal in their desire to just give away what has taken them sometimes many years to learn. Also you do not have a large cadre of racing boat mfgrs who are building boats for sale and have financial reasons for their boats, (which might or might not be similar to yours), to be successful in competition and therefore have blueprints for modifications to achieve that success.

The several folks who are in this situation really do not frequent this site near as much as they are on Hydroracer. Not for any reason that HR is better than BRF, but BRF has found a home with many whose racing career is over and more past history is discussed than present build information.

All that being said, I can give you the following information regards a DeSilva type runabout that was built by Krier Boats of Ollie, Ia. I campaigned this boat in the RB class that probably ran at the time, 5-10 MPH faster than what you will achieve if you use the motor/motors you are speaking of. That boat and motor combo would run right at 70MPH and I won a National APBA Championship with it in 1986. I did use a small transom mounted fin ON the boat that was originally a sponson fin from one of my Hydro's. It did accomplish what I was looking for which was to cut down on the tendency of the boat to slide sideways so much in the corner, but it also cut my speed by a mile an hour or so. Almost everything you do when you put more things in the water causes drag, which will slow you down.

My advice, which I am sure would be seconded by most experienced boat racers, is before you get excited about what might happen when you have no prior knowledge of how the boat is going to perform in various water conditions is DO SOME TESTING. Try to attend some races in your local and talk to the racers, examine their equipment, and if they have time before or after the race, strike up a conversation with them and tell them what you are doing and what do they think about how it might work and what to stay away from. Since you are being somewhat mysterious about the design of you boat and no photos are being shown, it is very difficult to help you.

Again the best advice I could give you is relax, slow down, and test, for all the reasons I have described and more besides. Take some photos and post them of the boat running on the water and hopefully you will get some help you are asking for, and also try HR. I think for all the reasons previously mentioned you might get more help from present builders and racers there.

AND AGAIN, RELAX. Testing to first determine whether you have problems that need to be solved, is much easier on the disposition than wasting time and energy trying to figure out the worst that might happen, that is only in your mind and imagination. If you have a problem found thru testing, then you can spend the time asking for help solving it, or working it out for yourself. Then YOU are the one they will come to for the assistance based on the knowledge you have gained thru this build.

I appreciate the advice.... and yes, I do get a bit frustrated sometimes, your right... I might need to relax a bit, that would definitely help (LOL!). But really all I would like to know is specifics in description of these fins as to how they protrude on the chine as far as relative angle and their general depth. It is really just useful info to have just in case it happens that I need them. I likely don't though. One important thing about testing a new boat is understanding the fundamentals of potential solutions if needed, or at least that is what I have thought. Maybe Im just a bit to particular where I don't need to be.

My boat is 10'2" length. The cockpit is nearly 60" X 21" wide. The hull is 44" wide with a 28" width bottom. It is flat up to about 48" from the transom then it forms a subtle "V". The keel line is long radius to the tip (bow) of the boat. The chines are 30 degrees rise up along the sides. The boat incorporates long radius lines all over for good dynamic purposes. I eliminated having a flat deck atop of the sides like most because I did not need them. I just made the deck as the side (going from the chine to the cockpit with no angles between). It planes right up easily holding the throttle at about 3500+ rpm. The prop gets hold good and I'm running neutral kick at 1" depth prop shaft center to bottom surface line. I measure this by placing a level flush on the bottom surface out next to the prop shaft, then I use a square to measure depth. I also use a level to compare the cavitation plate to the bottom to help determine if I'm tucked, neutral, or kicked out. I can run very well straight as fast as any. I will be practicing turns at speed once I get an idea of turn radius as in race courses and speed. I assume it takes about 8-9 seconds to make a turn in these class of boat. I suppose that bouys are 300+ feet apart on a 3/4 to one mile course, I don't know.

[champ20B]

Most guys did not and still do not use this type of fin.

The fins you are referring to were usually water ski size fins. Maybe 2-3 inches in length and 1 1/2" to 2" deep. When I have seen them on a boat they were usually placed on the chine as close to the rear and centered.

Craig Bowman of Brocolli Boats fame made some of his chines with a notch in them. It was roughly in the same position as a fin would have been.

Bottom line is if you have a well designed roll up, you don't need anything other than a fin on the bottom. A great, inexpensive roll up is a Trolian built Race Craft. There are bunches of them around and they are very easy to turn, at least I think so.

Tim

Thanks for the info Tim. I had watched and studied footage of these boats running and they don't appear to have but only a bottom fin as you said. I got a bit of advise a while back that got me confused as there aren't many pictures of boats showing certain features as these. I thought I would ask to be sure. BTW....those race crafts are real nice. I wish I had one. I had to build my own though. It was the more reachable option for me as I am experienced in boat building (fishing and performance), just not competition class racers. I can build a fast hull, but keeping it stable in a fast turn with a flat bottom is something I never thought I would be trying to deal with till lately. Thanks!

[champ20B]

I thought about when you said you went 5-10 mph faster than I would with the motors I'm using. I'm running a Yamato 80. I also have a 20 cubic inch Champion (SWANSON) hotrod like new and restored w/open stack.

As far as the hotrod, I agree with you on that. Those motors require specific upgrades to run well in B-Mod. But as far as the Y-80, those engines are very very powerful for a 20 cid rig. I hear good opinions and sometimes put downs on the Y-80, but I go by facts and I know I made a good choice on a motor. According to the APBA, every record in B-MOD for all course and Kilo are unbroken and were set by this particular engine. Yes, it was hampered in stock classes because of that ridiculous club foot and dull/flat edge skeg, but when you sharpen that skeg, put a sharp nose on the gearcase, and go with a high running prop, that engine is dynamite!! That is really what makes a mod Yamato modified. Unlike other engines, the Yamato powerhead is not the main focus for upgrade at all. It is mainly the lower unit that gets the go fast treatment. Yes, I know that guys like to use feul pumps, custom midsections, and those wonderful expansion chambers.... but that stuff is truly optional. Those things don't necessarily increase speed or horsepower at all. Only handling is mainly the reason if necessary. Down in Ecuador and Australia, those guys have beaten expansion chamber equipped Yamatos with those equipped with megaphones. Heck, over here, races are still won with megaphones still on hotrods, and OMC "B" frankenmotors. Expansion chambers haven't really proven nothing to me except to do the same job with less noise. And I imagine that if it weren't for technical catches implemented by the APBA, most yamato drivers would rather run horns on their motors as well. Actually, they come equipped with equally good megaphones inside the stock tower as is.