Tunnel hull design question

[MarkGugliuzza]

My son asked me a question about tunnel hull design. He was wondering what is the purpose of the fins on the top insides of the sponsons near the bows. All 3 of our boats have different styles. My PS295 has long low ones, his Woodstuff 32 has tall shorter ones and his Dumas Hot Shot Sprint has none.

Thanks

 

[Carl Van Houten]

They are really not needed. I don't use them at all. If you build the sponsns right, they are not necessary.

I guess if you were racing in a straight line like straight line record trials they would help keep the air that is spoiling through the sponsons from causing a vortex and aslo help the boat track.

Tommy had some on one of his custom stick-built tunnel boats that were towed out. He said he was trying to speed the air up over the deck. My thoughts were, don't help neturalize your lift. But that was not my project.

Some people use them to help a boat turn that doesn't have enough bite built into the sponsons and some people just think they look cool and put them on everything.

-Carl

 

[MarkGugliuzza]

Me and my son thank you for the reply and explaination. I've also had a lot of spectators at the pond ask me what they are for, now I have an answer for them.

 

[Mark Poole ModVP]

You would be suprised at what you can learn by "influencing" the airflow over any rc boat, hydro, tunnel, mono, etc. Many will say that it does not matter much until the boat gets past 50 mph but I have learned otherwise. Many rc tunnels had them because they were scaled after the lifesize boats. Prather and International Hobbies are good examples. Tunnels that tend to blow off while cornering would most likely benefit from having the fins.