Shark Fin Skeg ?

[silverghost]

I have a 24' inboard American Sker Eagle Ski-boat that has two bronze shark-fin skegs on the keel area about one third the way back fom the bow. The two 7" skegs are mounted on the center line of the keel about one foot apart. They look like bronze surboard skegs. The flanged bases are mounted in molded recessed areas in the hull glass.
Both skegs are the same size ~But do not appear so because of the camera angle. Hard to get a great shot under this low trailer! I just pressure washed the bottom after being in the salt water for five months & blew-off some Micron bottom paint !
This ski-boat turns at higher speeds like it is on rails !
What are these skegs used for ?
Do they help stability?
Or~ Do they work to help the boat turn by working in tandem with the
rudder by keeping the bow from skidding sideways?
I have seen these on inboard & I/O race boats in the 60s, 70s-80s~
Has anyone ever tried using these skegs on a Donzi C-16 or 18 ?
What would they do on a Donzi I/O ?
I would guess that they sadly also add some drag !

[VetteLT193]

I always wondered why they didn't use them on step bottom boats to help stop the turning issues.

As far as a regular I/O, I'm not sure what they would do... I imagine it would set up a fulcrum point for turning.

[mattyboy]

don't think the skeg/fin would like being aired out when a classic rolls hard to the side in a tight turn.
or another way to look at it if the would be beneficial to speed, handling or overall performance , someone would have done it over the 40 or so years that deep vee I/O hi po boats have been around ;) plus i think an I\O boat already has skeg ;)

[gcarter]

I think they are peculiar to competition ski boats.....
the ability to track straight when a 200# skier is 75' out to the side of you!
Or the ability to turn in your own length as you mentioned.
I've seen some ski boats w/3 of the fins.

On a different, but somewhat related, subject, many raceboats into the early '40's had bow rudders.
Since these boats had surface propellors, w/o anyway to control the inboard drive, outboard rudders didn't work well.
So the rudder was located just forward of where your fins are.
I believe Christopher Columbus Smith was the first designer/builder to use such a rudder.
It was sort of like front wheel steering in a car. The boat would definately follow the rudder.

[Barry Eller]

Ski boats use the skegs to keep the boat on track, especially necessary when a slalom skier is going down course on short lines. Keeping the boat in the middle of the boat buoys is critical to keep equal distance from the ski pylon to the turn buoys.

[Conquistador_del_mar]

I think they are peculiar to competition ski boats.....
the ability to track straight when a 200# skier is 75' out to the side of you!



Ski boats use the skegs to keep the boat on track, especially necessary when a slalom skier is going down course on short lines. Keeping the boat in the middle of the boat buoys is critical to keep equal distance from the ski pylon to the turn buoys.

Yep, they are there to keep the boat going relatively straight when the skier pulls hard to one side. I skied a lot behind my old 1971 Donzi 18' in the 70s, and I would pull the boat way off course with a hard pull - I broke quite a few ski ropes like that - ouch! We used the aft lifting ring since it was centered instead of the transom lifting eyes. Bill

[tmh]

Related to the last post, is the lifting eye preferable to the ski eye? The 18C does get pulled around quite a bit from side to side and it seems logical that the lifting eye is getting the hitch inside the boat. Is there any issue with the lift eye being strong enough to lift the boat but not being designed to be pulled laterally? I apologize for changing subjects.
T.M. Hayes

[silverghost]

My rear lifting eye on my "Benchseat" 18 project has the aft rear eye pulled into the deck from such a waterski episode!
Using the lifting eye is risky for anything other than lifting the boat straight up!
This is on the list for repair!
Better to install a ski tow eye on the transom with a good hardwood or metal back-up!
Don't let this happen to your Donzi !
See my Photos!

[tmh]

Thanks so very much before doing any damage!. I will contemplate whether getting the tow hitch inside the boat will improve stability as the boat does get pulled around more than I expected it would.
T.M. Hayes

[gcarter]

Many of our boats came w/two eyes on the transom located on either side of the drive.
A line tied off both of these eyes would be the perfect solution for skiing. The load would be split between the two eyes and perpendicular to the transom.

[mattyboy]

not all lift eyes are built equal

my 67 16 had a Y bracket that bolted into the wood of the transom, it held & supported the eye both vertically & horizontally. I skied off my 16 for 8 seasons @ 230lbs or more the previous owner for many more than that . no issues

also it had a ss ring that prevented the ring from ripping the deck silverghost pic doesn't show that ring

[silverghost]

Matty: That Ring you speak of is there ! It's still connected with three screws to the hunk of fiberglass deck that was ripped down inside the aft deck ! It has dropped inside that torn hole.
This boat also has the big Y bracket bolted to the wood transom core !
I would love to have seen how some prior owner damaged this deck!
I was told it happened watersking !
Did they have a circus elephant on the waterskis?
I guess I will never know?

[Marlin275]

Pulled every water toy and skier around
never any problem

[Dr. David Fleming]

Historically you are right on about the forward rudder and fins they are used on a lot of outboard racing hydros. They helped the early step hulls with stability issues - like hooking - guys like Garwood used them on the Miss America boats built in Michigan - first mahogany speedboats to break 70 mph and 100 mph. Big issue for today is the drag - like running a Bravo II on a race boat - lot of extra surface area dragging in the water.

Just think how hyper you guys are about a little old drive shower dragging - try a couple of big bronze fins.

Early Johnson racing outboards cut the skeg off of the lower unit of the outboard drive just to go that much faster - 1928 Johnson Giant Twin outboard had this and was the championship engine for that year.

Like running your bravo I with the lower fin broken off - seen a few pics of this. Could saw it off under the gearcase - wonder if anyone tried this?

Dr. d

[silverghost]

Who Knows what might have caused this lifting eye & deck failure ? !
Some peope can break anything !
Remember this was a salt water boat all it's life. The steel lifting eye supports do not look healthy !
It's possible that a punkey & rotten deck core here was part of the problem! This deck has some real core issues near any penetrations ie: vents, lifting eyes, nav lights, gas fill etc!
I will soon see when I pop the deck in the next week or two.
Looks like a partial if not complete deck re-core job.

[RPD]

When pulling a slalom skier you want the center of pull, ie the attachment point of the ski rope, located at the center of lateral resistance, which basically is approximately slightly behind the geometrical center of the contact patch as the boat is pulling the skier.... or you should put it as close to that as you can get it without interfering with the seating ... on a Donzi 16 or 18 this is going to be just behind the cockpit .... fins would be put directly under the tow point, or slightly forward or aft to adjust the center of resistance if necessary, but you would really mess up the handling on a Donzi and it would definitely slow you down ..... if you pull from the transom, a slalom skier can pull you all over the place, regardless of your power, unless the boat is very very heavy ....
PS: It's up to you to make sure the attachment point is strong enough.... I pulled a ski post out of a boat when I only weighed 150 (a long time ago!)