Ventilated Transom ?

[bh/]

Early '70's Craig Craft used a ventilated transom, until banned by the rules.
Did these transoms improve speed, improve stability , or both ? Did the air flow up, or down thru the transom,
ie; did it enter at the inside bottom of the transom and exit out the top, or vice versa?
Were they used on hydros too. What was the reason for banning them?

[DeanFHobart]

Early '70's Craig Craft I believe used a ventilated transom on its runabouts, until banned by the rules.
Did these transoms improve speed, improve stability , or both ? Did the air flow up, or down thru the transom,
ie; did it enter at the inside bottom of the transom and exit out the top, or vice versa?
Were they used on hydros too. What was the reason for banning them?

The air entered on the top side of the motor board and then vented out the bottom. I built an A Stock Hydro with a vented transom and set two World Records with it. I later built boats without it and went just as fast. It probably didn’t help much.

I do not recall the exact reason it was banned.

[ZUL8TR]

I think the idea was to help remove dead air behind the transom thus theoretically reduce air drag and supposedly go faster? The butt dino would find it hard to prove and there are so many variables around the race course that small lap time differences would be speculative at best.

Don't know about the runabouts but in the 70's I raced in 25ssh against these Craig Crafts hydros (Jeff Hutchins US-1 was one) with ventilated transoms and also Dave Rawson hydros that he designed an air induction system that forced air at the transom rear. Dave's looked cool with the intakes at the front of the cowl with tubes to the rear but neither seemed to run any better to me in competition those years.

Didn't know ventilated transoms were banned. Wonder why APBA banned the Craig Craft ventilated transom, APBA probably came up with some reason unknown to me. Maybe someone knows out there like Bob Wartinger?

[guedo499]

Two things:
1. Keeps the transom clean.
2. Made you look.

[bh/]

I am not certain they are banned. Maybe they just did not improve things ?
What brought this up was a discussion on tail gates in p/u trucks
and effect on aero drag; -apparently none .

[Ram4x4]

Mythbusters did a segment on pickups and driving with the tailgate up or down. The mileage was actually better with the gate up as opposed to down. They did a 2nd test, only this time with tailgate up, tailgate down, tailgate removed, tailgate replaced with one of those mesh tailgates and also with a bed cover. The tests with the tailgate up and with the bed cover did about the same. The tailgate down did the worst and the mesh tailgate actually did better than all of them by about 5%.

https://www.youtube.com/watch?v=r3aqHbD-O9E

[bh/]

-the 'mesh' tailgate , ie; a ventilated tailgate, reduced drag, so maybe there is some thing to it ?

[jon66w]

I built a CSR for John Puestow in the 1970's. It vented on either side of the Clamps and built sealed chambers down to chamfered slots on the out side of the transom that doubled as lifting handles. Looked cool and did keep the transom clean. Don't know if it helped speed and don't remember why it was banned. It was a conversation point after the race with a few PBR'S .

[csh-2z]

runabouts are not allowed to have any "through the hull air passages or vents" .

[Arcticracer]

Joe Price used this feature as I recall on at least some runabouts, prior to 1970. The date is easy because that was the last season we raced, and Joe was not working in our boat shop at that time, he was in Washington I think. He called it a "vacuum relief" transom. Details are foggy, it was a long time ago. Craig may have gotten the idea from Joe. I have been away from the site awhile, hope everyone is well.

[GrandpaRacer]

The size of the vent holes compared to the area of a transom would suggest to me that any speed advantage would be tiny and not worth the effort in building. Maybe they were banned (in runabouts) because they were weaker than non-vented John Adams

[Arcticracer]

I think you are right, never heard any proof that it worked.

[Black Sheep]

It was banned, and still is, in Stock Outboard Runabout only. I was nearly thrown out at Modesto in 1993 when I set the B Mod Kilo. I knew it was legal in Mod. I just took some explaining...
And to Guido’s point, the transom was always clean!

[CSR4C]

It was Joe Price that came up with the vented transom, he said the fact that it kept the transom clean, it worked. Jeff Reins built a runabout with some big vents in the deck, it was then the stock comission outlawed any vents on runabouts, air must go around the boat not through the boat.

[DeanFHobart]

Joe Price was very inventive in many ways in outboard racing when he was involved. He helped everyone that he was involved with to win national championships and set records.

[bh/]

The DEC issue of ProBoat, <www.proboat.com>, has an article referencing a sail boat
built by Darell Sorenson in 1992,
for research by Mech Eng/designer Alan Adler. who holds a patent on it.
It is a 14' cat, with two stepped hulls which are ventilated. He quotes speeds on a close reach @30mph+.
The hulls plane at ~10mph. Only hydro-foils and ice boats are faster.
The article says little about the vents, no documentation, but he does say they help in reducing
the wetted surface aft of the step.
This effect would not benefit one of our hydros or runabouts,
as there is no wetted surface aft of the transom
Runabout hulls in the '30s had stepped hulls, some with vents .
Unlimited hydro hulls of the '50s/60s had open ventilated sponsons,
but not sure why that was ? Speeds? I will write Adler and ask if he played with the vents,
as if he was seeing speed increases @30mph,
we should be @60mph+.

[ZUL8TR]

I was told by a inboard hydro driver years ago that ventilated sponsons were for water to enter to add weight to assist in planing over and the sponsons would drain out. No use for the venting after on plan. Maybe someone knows different?