X mono hulls

[John Finch]

What I have found is this..............with the prop close to the transom it tends to lift the entire boat out of the water. Running surface drive with the strut shaft about 5/8ths of an inch from the centerline of the shaft to the very bottom of the boat is a good starting point for the larger boats. If you go closer to the bottom of the hull the boat is lifted out of the water more. As you raise the strut up the boat tends to settle into the water more for more control. This is with the drive dog of the prop about 1 and 1/2 inches from the transom per a standard strut blade.

Now.........move the prop back 3 and 1/2 inches from the transom with an extended strut and all that changes. Now the transom acts as a hinge and when the prop causes lift it actually pushes the bow downward as the boat pivots at the transom. So, the extended strut acts more like a wheely bar on a car. When the bow comes up the prop is driven deeper in the water and it does not want to be deeper in the water so it pushes back and keeps the bow from lifting. That is the difference in the two setups. With the extended strut you change the depth according to how high you want the bow to ride. Also, I found in SAW trials that the strut length can be changed to adjust the ride of the hull rather than using trim tabs. Shorter strut lets the bow come up. Longer strut keeps the bow down.

 

[David Bryant]

great info Mr. Finch, thanks

 

[John Finch]

You are most welcome. Hope it helps.

John

 

[Ian Inverarity]

John, I think CG also has an effect on what strut height does too, my 44" Seaducer had a Seaducer strut which was short, but with a relatively forward CG running the strut deeper on that boat would push the bow down in the straights. In the turns the effect was the opposite tho. I did try a long strut on my 46" Kingcraft many years ago, and I didn't like the handling so went back to the short strut. Interesting stuff tho, my next gas boat will have a longer strut to try.

 

[John Finch]

John, I think CG also has an effect on what strut height does too, my 44" Seaducer had a Seaducer strut which was short, but with a relatively forward CG running the strut deeper on that boat would push the bow down in the straights. In the turns the effect was the opposite tho. I did try a long strut on my 46" Kingcraft many years ago, and I didn't like the handling so went back to the short strut. Interesting stuff tho, my next gas boat will have a longer strut to try.

Ian,

Yes, the Seaducer works well with the shorter strut but as you said the CG is more forward. The Seaducer is the only mono I have seen in production with that forward CG. I made a TwinCraft Pro 41 that used the Forward CG that ran like the Seaducer. I used the short strut like the Seaducer and used the rudder to dial in the ride. With the rudder far from the transom the boat rode too lose and blew off the water. Moving the rudder closer to the transom brought the bow down. The pro boat was made to work like the Seaducer so did not have trim tabs. While the boat was faster than my standard hull the problem with the forward CG was an occasional nose dive like the seaducer. I later added a spoiler to the transom and kept the boat from nose diving. If the transom does not leave the water the boat cannot do a nose dive. It was not a wing. Wings are not legal. It was a spoiler, which is legal. I gave the boat to a buddy who races every so often and it runs 65 mph no problem with a 67 pico, The pro boat is not an available boat to the public. It is also a very ugly boat, so no one would want to buy one if they were available.

Jerry's Seaducers are far more pleasing to the eye if you want to go to the forward CG.