Hull is "Hooked" at the transom ???

Hello everyone.

I've been browsing around on another forum; http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=60859
and stumbled onto a thread that caught my eye. The thread itself is about having a weak moment and "dragging home a project".

In the thread, the member (rivet) states:
"the boat was not supported correctly and has a slight hook at the transom"

Later in the thread (pcford) states:
A one inch hook will produce a ride that is wildly dangerous!

Then I post:
Can you explain ?

The reason I ask is this: I bought a 1960 17' plywood power boat 3 years ago. Before I bought it, I took it for a "TEST" ride. Everything seemed to check out, with the exception of some apparent damage to the keel just below the stem where she had obviously been beached in the rocks. Anyway, after reading this thread, I remembered that while powering down the lake at full speed (approx. 35 mph determined by the boat following us) that the boat would suddenly do a "U-TURN" for no apparent reason nearly throwing me and the seller out of the boat. It did this several times. I had originally blamed this phenomenon on the ancient cable & pully type steering which incorporated springs on each side (near the transom) for the cable tension. (These springs had been jury-rigged in a redneck fassion and included a section of "dog chain" ???). I figured that a new TELEFLEX steering system would fix this.

After getting the boat flipped over during restoration I realized that the bottom of the hull (on both sides of the keel) is caved in. This is just in front of the transom where the boat sat on top of the rollers. I have since re-structured that trailer, removing those rollers and installing "adjustable" running boards that are 7' long, positioned directly under the stringers and long enough at the back end to extend just beyond the transom thereby supporting it at the transom and under the stringers like it should have been all along.

Is this "caved in" portion of the hull what you guys are refering to as a "HOOK" ?
Is this possibly what caused the boat to act so erratically ?

:?: ??? Does anybody here have any input on this ??? :?:​

 

"Hook" is the description of the hull when the bottom and stern buttocks do not leave the transom of a planing hull in straight or convex (referenced to up) lines. The lines of the keel and buttocks are concave (referenced to up) and the transom is lower that the hull immeaditly before it. It is a smooth transition unlike an applied planing wedge. In lightly framed boats, it is caused by the poor blocking aft allowing the weight of the transom to be supported by the hull skin alone which gradually droops over time. If the whole hull is poorly supported then the much more common "hogging" occurs where the whole keel is forced in to a concave (referenced to up) shape.

Some hulls are designed with hook, such as the Simmions Sea Skiff; and some have planning wedges applied.

Hook effects handling by causing a high pressure right at the transom. This forces the bow down (which is why it is sometimes designed in). However, if it forces the bow down too much, the center of drag can be forced forward increasing the drive-drag destablizing couple which leads to stability issues in the lateral plane and the "U-turn" effect you describe. Note that the amount of force generated by the hook, the instant center of mass, and center of lateral plane are both speed dependent, so the stability can be very speed preciptious.

 

jehardiman

Thanks for your reply. Very descriptive and detailed... posibly more than my little brain can handle

I do believe that I understand what your saying though. Your basic answer to my biggest question then would be YES ! The "HOOK" in my hull is more than likely the cause of the boats instability at higher speeds because the transom is being forced out of the water causing the boat to plane (make contact with the surface of the water) about or near mid-ways up the boat rather than directly at the transom. Did I say that right :?: :?: Kinda like what happens when a pilot changes the pitch of the tail flaps on a plane, tipping them down. The tail comes up (sorta speak but, not really) and the nose goes down :!:

 

If the center of gravity is ahead of the center of drag on the boat, the boat is stable; if the center of drag moves in front of the center of the CG, then the boat becomes unstable and will swap ends.

I first discovered this while flying model rockets - the cure for an unstable rocket is to add mass to the nose (wedge some epoxy putty inside the nose cone). Not sure what you could to to fix a boat, maybe add a fin under the transom?

 

Tja

Hello, I had a customer with a 12ft. speedliner leave the boat on a roller trailer for over 10 yrs. making four indented areas about 10in. x 18in. I removed the paint down to bare wood and filled the areas with thickened epoxy. Then i faired the bottom , coated with epoxy primer and paint. Problem solved. Hope this helps. Sincerely, Tom.

 

VKRUE, an easy way to explain "hook" Imagine sighting along the bottom of your boat from the back, the stern (transom). If you put a straight edge on the bottom running forward towards the bow, the bottom should be straight untill you get about 1/3 the length of the bottom where it starts to curve up. This distance varies from boat to boat. However if the bottom is not straight as it approaches the back end of the boat then you have a hook or a rocker. If the bottom curves down as it approaches the back it is hook. If it curves up as it approaches the back it is rocker.

Imagine one of those back scratchers with a long straight handle and little curved fingers on one end. The curved fingers are the hook. On most planing boats the back 1/3 or so of the boat should be straight, with a nice sharp edge at the transom. This allows the water to flow cleanly off the bottom and gives you that nice flat wake behind the boat. As was said a hook will force the bow down. if the hook is only on one side it will make you turn toward that side. If it's on both sides if may bury the bow causing the boat to rotate around the bow: the U turn.

 

Allright............ thanks guys.

Tja:
Am considering your approach but, I'm going to try to force it out first.
(GENTLY)

Understand completely Ike. Thanks again guys.

 

I have a 1995 18.5 foot bass boat and I noticed that in front of the transom, directly in front of the outboard that the hul has a 1/2" hook to it...and I am having overheating problems that are believed to be caused by turbulence...can it cause that?..and how do I fix it?

 

On a bass boat that's not a hook, that's a pad. Most bass boats had a pad just forward of the transom, which at top speed becomes pretty much all the boat is riding on.

What you might want to do is adjust the height of the outboard on the transom. Try lowering it an inch and see if the problem goes away. That should lower to water intake into less disturbed water without affecting the top end, and it should increase your acceleration out of the hole.