Installing sprayrails & strakes on mono's ?

[riggerman]

Hi all over the past several years of buiding and running 3 different versions of 6-8 cell mono' hulls 23'' in length 6 3/8'' beam and 20 degree's of vee i have experimented with different sprayrail and strake configurations on the first 2 hulls i built i installed spray rails on the chines and 2 strakes on each bottom side off the hull spaced evenly the 2 closeset to the keel terminating at 5'' from the transom and the other 2 further up terminating at 3 1/2'' from the transom all strakes being faired in to the hull bottom .On hull #3 i did not install any spray rails at all and 2 strakes one on each side off hull bottom half way up between the keel and the chine starting at a point 8'' from the bow and terminating at the transom. Running all 3 hulls i really did not notice any signifigant difference off the boats running in the straights or in the turns im estimating the hull speeds where between 25-35 mph. I have observed on mass produced fiberglass hulls also have different variations off strake and sprayrail configurations are used e.g. 21'' Bandit Pistelero has no spray rails and 2 strakes centered on hull bottom and terminating at different distances from the transom while other manufactures boats have sprayrails and 3 strakes on each side off the hull bottom and pretty well running the length of the hull. Do's postitioning of strakes and instalation of sprayrails have to do with the boats anticipated operating speed ? What factors determine the location of strakes and if spray rails are required ? Regards Andris Golts.

 

[PinkishPanther]

I have mainly worked on strake patterns for gas monos 44" and over. But, what i have learned is that the strakes help the boat get onto plane quickly. When the boat is running at 3/4 to full, the hull itself will keep the boat up out of the water. Usually the water line is lower than the strakes at this point and its only running on the back 15% of the keel.

There is some effect in the corners depending on you design. I have one that stops the strakes 2" before the COG. It performs perfectly in the straights but gets squirly in the corners and wants to hook into the course. I haven't fully tested it, but its either the strakes or the prop was too low. I'm hoping its the prop height. In theory, the strakes stabalize the cornering because it will act as a fin in the water. But, I'm not convinced it really is enough to mater when you have a big turn fin on the transom corners.

One problem with designing these monos like the real ones (as many do) is the power to weight ratios, bouancy and performance are all wrong. The real ones would probably perform the same if they went 700 mph. If you look at them closely, most of those strakes go all the way to the keel. They are there for lift to keep the heavy hull out of the water when its running.

So, with this. I'm getting to the point now that I don't think the strakes are even needed. I have seen/heard a couple wooden gas monos that dont bother with the strakes at all and still perform perfectly in 'race water'.

My guess is that your boat is small and light enough that those strakes aren't doing anything.

Phil