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View Full Version : Semi planning hull design mods?



Mhall222
08-11-2021, 12:10 PM
Now his post is not exactly related to screaming and flying but it is posted in hopes of improving performance and speed on this project. I acquired the original hull molds for two Johnsen skiffs that Jay white used to produce down in Central FL. The molds were in horrible condition so a plug was laid up in one mold before the mold itself was scrapped. This plug has worked me to death trying to make it as straight and symmetrical as possible and I am getting closer to having it ready to make a new mold. Before I make a new mold I wanted to explore possibly making some minor changes to improve the performance. First off the hull as built in hook which does drive the bow down but also most of these boats experience hull flex which causes the bow down ride to be even more pronounced. I am going to be installing stringers and a floor system that will greatly improve any flexing issues these hulls may have had. My question mostly relates to the trailing edge of the transom, the original hull had a nice 1" radius which would be super easy for when laying the hull up but wouldn't that hurt its performance somewhat? I have seen 3-4mph gain from hulls having the trailer edge of the transom sharpened. On a boat that would normally only run 20-25mph those gains would be substantial. Anyhow this hull is not designed to be fast and with it being a semi-planing style a sharp trailing edge may not help much. I was curious of your thoughts. Also the ribs that run down the hull, they are rounded over and not sharp, wouldn't they perform better in turns if they had sharer edges? I even thought about maybe modifying them to be actual lift strakes but I really do not want to destroy the vintage looks of this design with too heavy of modifications. I want it to still be a johnsen skiff but just highly refined.

Thanks
Mike

XstreamVking
08-11-2021, 12:26 PM
Son and I re-purposed and re-built a 1967 Larson runabout recently. Turned it into a skiff. We straightened the bottom and sharpened the edges. It has a cool bottom. Pics on here you can see... After all the mods and work it goes 40 with a 50 hp 2 stroke merc. We are happy with that! You might get some results from a transom edge clean up. Depends what hp (i'm guessing 25?) I remember riding in one of those and yes the bottom did flex under your feet. You might benefit from core mat in the glass layup to stiffen the bottom. Also some foam core strips in the sides would help.