Thoughts of adding strakes

[XstreamVking]

Boat wants more bottom rocker. Or more weight to the rear.

[CharlieN]

The fuel tank is in the bow and has about 15 gal on board. When I rebuilt the hull I made space for a 20 gallon tank under the floor in the last 40" of hull. I just have get around to welding up the tank.

At that time I worked all the hook out between the inner strakes, out at the chine it has hook but that does not affect this.
Possible there is a touch of hook and this will be addressed this winter.
But you are thinking adding some rocker.

I have 8" setback and for the most part I am running a 25P Predator that is nice and sharp. It does not like to be run high and trimming up is non responsive. Clearly that prop can not pick this hull up.

So your thoughts are on rocker rather than overall lifting surface to loosen the hull up.

[CharlieN]

My uneducated opinion would be to make a pad, but it does take some ability to drive it on the pad! Less boat in the water, time to fly!!

I keep rolling my thoughts on building a pad.
This hull has a protruding keel under the forward 2/3 of the boat, part of what made them one of the better ski boats back then.
A few years back when the core was being rebuilt I gave thought to filling the bottom of the V and glassing it over in prep of flipping the hull and cutting in as needed for a pad.
At this time the hull is fully foamed in so digging in to do any structural work inside the hull is not desired.
This is where my thoughts have been on strakes, obviously if strakes are added right near the centerline they would effectively be a pad.
If added out a little ways would add lift with a wider running surface, better for some of my friends that also run the boat who would not have the finesse to balance the boat on the pad.
I will be out under the hull later this morning measuring if the running surface is flat or not. This will be important and will not have a final assessment till the hull if turned over and on the work cradle.

[XstreamVking]

Try a 24/26p chopper if you can. It will drop the stern, lift the bow. Lets you run the motor higher and trim up some. Get all the weight out of the bow. Boat ride attitude is level, motor is level. Running up on the strakes like it is designed to do. Just needs tuning. For what it is, performance is good now.

[CharlieN]

For the chopper, I presume the larger ear version?
I see a fair bit of talk about the Tempest. One just went on ebay that I considered grabbing. Only reason I did not was that I want to swap powerheads before prop testing.

[XstreamVking]

I like the tempest props. Good bow lift. I have one for my stream for running with 2/3 passengers or going in choppy salt water areas. Good all around prop. A chopper, big or small will surprise you with the change in the boats bow lift at speed.

[CharlieN]

Just checked with a 4' straightedge, looks to be .090" hook with the downturn in the last 8" or so up near the inner strakes. The port side is a little less, call it .060-.070.
Down along the keel is straight for about a 10" width.
I did not check in front of that to if or what curve is forwards of this.

[CharlieN]

I like the tempest props. Good bow lift. I have one for my stream for running with 2/3 passengers or going in choppy salt water areas. Good all around prop. A chopper, big or small will surprise you with the change in the boats bow lift at speed.

It will be nice to get a prop that responds well. The Predator has a nice cruise but cavitates easily. Highest I can run the motor is about 3½" below. This is with stock case still. Seems happiest about 4" down.
Part of me wants to buy a prop now since I will be running about 60 miles on the Ct river run a month from now. The other part of me has been saying to wait till the power has been added.

[CharlieN]

I like the tempest props. Good bow lift. I have one for my stream for running with 2/3 passengers or going in choppy salt water areas. Good all around prop. A chopper, big or small will surprise you with the change in the boats bow lift at speed.

What are your thoughts between a 3 blade or 4 blade Chopper?

[XstreamVking]

Never ran a 4 blade chopper style prop. No help there.....3 blade big or small choppers can be surfaced and will give tons of bow lift. Only boat I run a 4 blade on, is my flats boat. It's a predator 25p with xtra cup and works really well for low and mid range not very good for top end , gets right on the limiter. Top end w/predator=70. Top end with 3 blade 27p tempest 78 mph. Same r's on top, just slower to plane with tempest vs predator. Same flats boat with a labbed 28p lightning ET is 83mph, at 5850 r's.. IMO re-prop after power increase.

[CharlieN]

I did just purchase a 3 blade Chopper that has some leading edge nicks on it. There is a nice looking 4 blade out there as well.
I will freshen the 3 blade and run it and see how it runs.
I have wanted a 4 blade and have a Composite 23 pitch that is impressive out of the hole. This is what I run in stump and rock infested waters. I also just tried a 4 blade 25P shooter, I am thinking the hub is spinning in it, the prop is horrible. At 4K the predator is running over 50, the shooter was 42 at best. I would occasionally get a vibration and the boat would slow down. I never opened the throttle in a 10 mile run last weekend with it.

[Jimboat]

This winter I intend to flip my 20' Glastron in order to refinish the bottom...When I bought the boat it ran 47mph and with the work I have done it tops out at 62 now. My question, I have been giving thought to adding a pair of strakes inboard of what is there. The existing inner strakes are 26 apart on their outer face. What I do not have a feel for is what differences in handling, ride and performance would one expect from the added lift?

Charlie - cool project!
If your desired purpose for mods is to increase speed, then increasing lift on centerline of the hull can help you. Inner-located strakes will help accomplish more lift, but remember that the bigger you make the strakes, the more exposed edge there will be as a trip hazard. Of course, the need for additional speed will come with different handling characteristics, particularly in turning, and a rougher ride. it's always a compromise.

I keep rolling my thoughts on building a pad.

I think that you're right that inner-located strakes are very similar to a pad. you might find that a center pad could add some desired lift, and might do so with a lesser exposed trip edge. Here's an article on pad desgin and performance that might be of interest.

This afternoon I got a chance to get on the water with a friend being able to snap some pics. These two pics are of the boat running the high side of 61mph, all she wants to do at this time.

From your pictures, it appears that there is quite a bit of boat in the water at the speed taken (the outer strakes are wetted at the aftmost locations). If that is top speed, then you might benefit from a prop that generates a bit more bow lift and perhaps move some weight to lighten your bow. The long wetted length of the hull with this setup is adding substantial drag that reduces top speed.

Sounds like a fun project!

[Tinkerer]

I had a 1977 CVX 18 that had a pad bottom and was very stable even in the rough.
My fuel tank was in the bow also - move as much weight to the back as you can. Get that tank out of the bow.
If you want to modify it add a pad.
OH and it did mid 90's

[CharlieN]

Jim, thank you for looking this over and your thoughts, I do not have a desire for wide strakes, if I add strakes they will be equal or narrower than what exists. Call it similar to a 7" wide pad. At this point if I add a pad it would be just that, added. I do not have the desire to remove the new floor, foam and center stringer to do glass work from the inside. I have access to the aft 40" of centerline but in front of that would be complex.
So this would present me that either the pad or strakes would give similar trip edge.
My boat gets driven buy people that I am sure would not concentrate on driving at high speeds which leads my thoughts that the wider base of strakes would be a easier to drive although somewhat less performance potential than a pad.

One other thing my thoughts are on is notching the transom. I have 8" setback now I presume that acts to add more setback?
I see thoughts of the notch when researching the 21' hulls.

I will have a Chopper prop here on Tuesday, probably just as the rain arrives but I will run it soon as I can to see if it can lift this hull.

Tinkerer, looks like you had that 18 running right well. Out of curiosity about how much power did you have in it?
My next project will probably be a 21' car powered boat which will start out with an LS motor in the mid 300 but can climb easily from there.

On this hull I am installing a 20ish gallon tank under the aft floor that will be in addition to the front tank. This way the front tank can be left empty till the range is needed.
When I rebuilt the structure I located the battery, oil tank and jack pump port side just behind the rear seat, these could be moved back 3' feet or so. Other than lighter front seats there is no easy to move weight.
The boat at this time is 390# lighter than when I bought it.

[Jimboat]

Charlie, what does your boat weigh?