1/8th Scale Hydro Air Trap Depth?

[Ken Smith]

Hey Guys,

I'm in the process of building a ML Boatworks 1/8th scale 8701 hull and have a question about the depth of the air trap. The kit puts the belly of the boat almost an 1/8th of an inch with the lower edge of the non-trips. I also have a Faulk marine and was comparing the bottoms and the depth is very different (see pictures below). The belly of the Faulk is pretty high allowing a lot of air under the boat. The ML kit has almost no room for air under. Now, I think I remember this is a recent change in design based on the faster speeds of today's boats? I just want to make sure. If not, I'll need to modify the ML kit to allow for a higher belly like the Faulk. Thanks.

 

[Brian Schymik]

Boy Ken Im with you

that doesn't look quite right

 

[Ken Smith]

Yeah but I think I remember reading somewhere that you don't need to pack as much air under the boat now days with the faster speeds. Also, I recently purchased an 8401 ML hull that was already assembled, with bottom installed and it too is low. I know Mike made a lot of improvements to his kits and I'm thinking the lower bottom is one of them. Just looking for some confirmation on that. I may post this thread in the ML forum as well. Thx

 

[u60]

Ken, it looks to me that you may have glued the bottom of the boat to the belly pan instead of splitting the bottom to go around the belly pan. Des that make sense? In other words the break in the bottom is farther back, or should be farther back than where you have the seam now. The center section, where the belly pan should be will be lower than the bottom itself. If you look at the engine well frame, is there a dotted laser burned line depicting the actual bottom angle? Fred

 

[Ken Smith]

Hey Fred,

I was actually thinking the same thing about the belly pan break and was also looking for the laser etched line on the sponsons or cockpit sides that would indicate this. However there are no lines that indicate an incline on the belly pan. In fact there is a laser etched line that runs from the transom to the back of the sponsons but it is completely straight and about 1/8th inch from the bottom. This is where the current bottom is positioned now. Tried to take a pic below. Thx.

 

[Hydro Junkie]

I'm not an expert on the 8701 but, after measuring the 8806, I found that the bottom is 4" above the bottom of the nontrip up to the break and the belly pan is roughly 3" below the bottom forward of the break. Since the 8806 was based, to an extent, on the 8701, I'm thinking the layout of the bottom is probably similar. Something else that I've found is that many of the canard equipped boats seem to have the bottom break roughly 86" forward of the transom with the bottom 12" above the bottom of the sponson inside at the sponson transom. I've changed the bottom profile on my Executone build from what Roger drew to these same approximate dimensions, also measured on on the 8200 hull, to decrease the amount of air under the boat as it drops the bullnose down by around 1/2" from what is drawn on the plans

 

[Mike Luszcz]

OK, Before this gets out of control, let me explain the process. Yes, the air trap was changed, on purpose. With the higher speeds, its just not needed. The change in break point has also made it look a lot different than it really is. You still have a 1\" sponson depth vs. transom depth...just like always. We are finding more and more every day pointing to removing the up angle as much as possible is making for a much more stable ride. Techniques like this..and more, are why the current IMPBA Saw record is over 100mph...and before I get jumped...the SAW record had even more tricks as we all know SAW and heat racing is much different. As much as I like using the Newton Plans for a tool, building a hull to them these days with the faster speeds will keep you on your back more than finishing a race. There are really two choices you have...build it the way the full size was, and more than likely have stability issues, or make these changes to the bottom side of the hulls...which is perfectly legal per the rules...and have a boat that can be faster, and more stable. The air trap being reduced, was to keep just enough air hold to keep the rear of the boat up due to the rear wing weight. This boat Ken is building has rear shoes that will need to be added as well which will help with the rear load. I have started doing air trap elimination on hulls with simple \"behind the sponson transom\" designs, ie: wingless hulls. I guess it can be taken for what its worth, but with the results in SAW and my sport hydroplane lineup in heat trim, not moving to these ideas, to me, and the racers who have already bought in, is just nuts!

Another thing I have noticed on the sport hydroplane lineup is my Center of Gravity is 2-3 times further back than other hydros out there. Why is this important having a CoG not at 1\", but 2.5\" or more behind the sponson transom??? Easy, have you ever hit a wave wrong, bounced the bow, only to see it come off and nose dive? I have, but with your CoG so much farther back, it comes off the wave, rides level, lands level, and keeps going. But is it fast you might ask..I don\'t know...you tell me... I am running the 39\" sport hydro at 68mph, with temps coming back cool, and I have yet to blow the hull off no matter what the conditions..oh, and that is radar-ed speed, in heat trim. You just have to realize one thing, while our hulls are 1/8th scale...water and wind is full scale, and the speeds are well beyond 1/8th scale...so how can designing around the full size hulls be practical. I have yet to understand that! Hope this clarifies my thoughts, along with those guys who have proved this works time and time again. I definitely don\'t stand alone on this. Sorry if this post sounds rude, as I am not trying to be. I am passionate, and wish the best for those who choose to build from my kits. I also like keeping some of these ideas a little more secretive, but after being called out on a few threads, maybe it was time to let people know whats on my mind.

In closing, I want to make a prediction. There is a T4 being built on this site right now with the Newton/ full size ram wing angle in all the wings...I predict, along with others who I have talked to, that the boat will be no good over 45-50mph. Its a beautiful kit and build, but its going to be a kite. It is a shame to spend a year designing and building a hull like that, only to realize you messed up following outdated ideas. So, everyone should sit back and see how well designing around 1995 ideas will turn out. (Oh, I received a nasty PM from this person a year ago which is why I even brought this up..I will be watching.)

Anyways, that is all. Mike

 

[Greg Hahn]

Mike,

So I take it you are lowering the boat bottom area to decrease air trap, are you also keeing the overall aerodynamic foil the same thickness/shape? In other words is the transom and deck staying the same height? If not, by increasing the height of the center section airfoil you're also increasing the lift generated which will counter the effect you're trying to create limiting air trap.

In conversations with some of the full scale guys, managing the lift and lift balance is more important than air trap but as you mentioned water and air do not scale down consdering the weight difference. Weight is the reason water and air dont' scale out, our 1/8th scale boats would need to weigh 800 lbs for those parameters to scale.

gh

 

[hugh hargett]

Heck no dont modify Mikes kit! Its designed for not blowing over alot more than the older designs. Right now Mikes putting out the hulls to have . DO NOT DO IT! You will notice others start to copy HIS designs - as it already taking place.

 

[Mike Luszcz]

Greg, Most of the air trap rail depth reduction does not affect the non trip side, so I can easily reduce the air trap without changing the pan depth or non trip angle. IN THOSE INSTANCES that the pan has to be lowered due to non trip angle where it ties into air trap no conforming, I also deepen the sponson transom depth to keep a 1\" overall depth. I know what you mean by lowering the pan and not the sponson depth as it increases velocity, and will eliminate the effectiveness like you said. But I am doing the total package with this change. I once saw a post by one of the people above that they widened the tunnel, and shallowed the sponson to reduce air flow...Nothing is further from the truth!!! They actually lowered the pan, increased velocity, AND increased the tunnel width which helps create even more surface area to create a wonderful SNAP effect as the boat kites off the water. If anyone would like to just call me, or the guys who put their input into these changes, please feel free (252) 717-6282. Its so hard to express all the changes and why they were done on a typing forum. The testing and results are not lieing. Everyone wants to keep trying to find ways to falsify whats going on, but I have the answers to correct this. A lot of dedicated racers that have done this racing a long time willingly gave me their hard earned data and knowledge so these kits would be a help and not a problem. This is not all just coming from me.

The problem is so many have found ways to bandage up the problems for so long they are unwilling to accept that there is a better way to do this. Another thing, you can still have the hull fly if you want, just add a touch of up angle to the strut to lift the bow, its not that tough. The difference is that \"flying\" is now a controlled equation, not something that you have to add lead to control. The funniest thing I see, is windshield wipers or other air flow blockers added to the center section bottom to help keep the boat down, yet people do not understand why the bottom of my sport hydros have a built in air brake!! Its so simple to understand, you just have to sit back and review the total package of changes! Be open minded!

 

[Ken Smith]

Hey Mike,

Thank you for the detailed explanation. That really helps. I'm very sorry. I feel like I may have thrown you under the bus with this question. That was not my intent. This thread is about my own inexperience in building and I was honestly looking for some guidance. I think its worth mentioning that Mike offers a great service to those people, like myself, whos only option of entering the scale sport would be buying used or pre-built hulls. I will always be amazed (and envious) of those brillaint folks who can scratch build a scale. Trully, it is amazing. But Mike has brought the sport to the masses with his kits and it sounds like he is honestly trying to make them more competitive by today's standards and simultanously helping the sport to evolve. Mike, I hope you continue to offer the scale kits well into the future. You really help guys like me

 

[u60]

Mike- I didn't realize that you had made these changes to that hull/kit. Ken's pics makes sense now that I know that you had made the changes to the bottom. I was thinking that the kit was kinda "as drawn" and so it looked different.

Most of the scale racers in the NW have been changing the bottoms of the 1/8 scales for years. In other words reducing the lift. There are different ways to do this and acheive the same results.

Ken, there you have it... the design was altered from the original drawings to improve handling. Keep building your on track!

Fred

 

[Ken Smith]

Yep, onward and upward Thanks everyone. We can close this thread now. My questions have been answered. Cheers!

 

[Samuel Hagan JR]

Don't close the thread!! This is some really good information. On the subject of Air Trap Depth Im in the process of finishing up the rear Skis on my T-6. How far from the bottom should I add the little steps too. Right now there flush then im going to add the steps. Should I use 1/8 " or 1/16".

It's also a ML boat. The bottom is where it should be. Was wondering how far down it should be from the bottom.

 

[Joe Wiebelhaus]

Spot on..... perfect explanation, leave it as built.

OK, Before this gets out of control, let me explain the process. Yes, the air trap was changed, on purpose. With the higher speeds, its just not needed. The change in break point has also made it look a lot different than it really is. You still have a 1\" sponson depth vs. transom depth...just like always. We are finding more and more every day pointing to removing the up angle as much as possible is making for a much more stable ride. Techniques like this..and more, are why the current IMPBA Saw record is over 100mph...and before I get jumped...the SAW record had even more tricks as we all know SAW and heat racing is much different. As much as I like using the Newton Plans for a tool, building a hull to them these days with the faster speeds will keep you on your back more than finishing a race. There are really two choices you have...build it the way the full size was, and more than likely have stability issues, or make these changes to the bottom side of the hulls...which is perfectly legal per the rules...and have a boat that can be faster, and more stable. The air trap being reduced, was to keep just enough air hold to keep the rear of the boat up due to the rear wing weight. This boat Ken is building has rear shoes that will need to be added as well which will help with the rear load. I have started doing air trap elimination on hulls with simple \"behind the sponson transom\" designs, ie: wingless hulls. I guess it can be taken for what its worth, but with the results in SAW and my sport hydroplane lineup in heat trim, not moving to these ideas, to me, and the racers who have already bought in, is just nuts!

Another thing I have noticed on the sport hydroplane lineup is my Center of Gravity is 2-3 times further back than other hydros out there. Why is this important having a CoG not at 1\", but 2.5\" or more behind the sponson transom??? Easy, have you ever hit a wave wrong, bounced the bow, only to see it come off and nose dive? I have, but with your CoG so much farther back, it comes off the wave, rides level, lands level, and keeps going. But is it fast you might ask..I don\'t know...you tell me... I am running the 39\" sport hydro at 68mph, with temps coming back cool, and I have yet to blow the hull off no matter what the conditions..oh, and that is radar-ed speed, in heat trim. You just have to realize one thing, while our hulls are 1/8th scale...water and wind is full scale, and the speeds are well beyond 1/8th scale...so how can designing around the full size hulls be practical. I have yet to understand that! Hope this clarifies my thoughts, along with those guys who have proved this works time and time again. I definitely don\'t stand alone on this. Sorry if this post sounds rude, as I am not trying to be. I am passionate, and wish the best for those who choose to build from my kits. I also like keeping some of these ideas a little more secretive, but after being called out on a few threads, maybe it was time to let people know whats on my mind.

In closing, I want to make a prediction. There is a T4 being built on this site right now with the Newton/ full size ram wing angle in all the wings...I predict, along with others who I have talked to, that the boat will be no good over 45-50mph. Its a beautiful kit and build, but its going to be a kite. It is a shame to spend a year designing and building a hull like that, only to realize you messed up following outdated ideas. So, everyone should sit back and see how well designing around 1995 ideas will turn out. (Oh, I received a nasty PM from this person a year ago which is why I even brought this up..I will be watching.)

Anyways, that is all. Mike