New boat problems

I am confused between the Breezecraft and the Johnsboat.

The Breezacraft look nice. I have no doubt about the claims. Still interesting that they find they go better with a single offset drive. Supports what I found with the wave pattern from the symmetrical hull. Still a trough at the outboard at the 6 knot mark.

NZD6000 for the sportcat is a good price. It would be nice riding in chop.

I guess too far from you though.

Rick W.

 

Hi Rick thanks again for your interest, as soon as my boat is out of the water I will post some detailed shots.
I intend to completely remove the wave piecing protrusion & extend the hull falward so they at least reach the front of the boat.
I hope you can help me with the new shape but I will also fit a new transom so the motor can be slid along just in case we cant get the boat to work with it in the centre.
All help greatly appreciated - thanks Mart.
PS Yes a good price for the sportcat but it looks like a single skin, not like most poly boats? Still it would be a great base to work from & fit out as you please.

 

If you give me a better idea of what you want to do with the boat then we can work through some ideas. Would also be useful to know what construction techniques you use/prefer.

Information like the total weight, the intended speed, the preferred outboard, the typical operating conditions, etc

I have not evaluated the program I use for the wave analysis on hulls similar to yours hence my interest in your feedback on what you actually observed.

The Breezcraft hulls are certainly a good starting point. They might have tendency to yaw in a trough but should be a nice hull for 20 to 30 knots in chop. Also lots of buoyancy in the ends so stable platform.

Rick W.

Rick W.

 

Ok well the boat was built with one sole purpose - spearfishing.
We are free divers (no tanks) so I had this idea to fit the floats under my boat for several reasons -
1 - to make the boat more stable when we get in & out over the side to dive.
2 - so the floats made a step along the length of the boat so we have easy entry to the boat from the water.
Both these aspects work very well, the main dive spot is a small group of islets about 3 miles off shore, there is very shallow water through some of the passages & we also dry out the boat for shore diveing.
A cat is a perfect tool for this type of use, the motor is new this year & I would loose out huge if I tried to sell it or part exchange it for twins motors.
On that basis I would like to keep my motor at least for this season.
Here are some pics of the build, I will be using the same techniques to altar the bow ie glass over wood or foam & sand down, top coat with gel.

 

So this is what my hull look like & two possible designs for the mods?

 

Sorry Rick forgot to say - we did seem to get the boat on the plane, my mate sat in the back to get the nose up & we ran against the tide in a small chop. The boats speed went up to about 22mph but there was so much spray comming out the back it looked like a jet boat, the water was being separated by the leg & jetting either side. however the motor at that time was sunk very low , cav plate about 4 " below the hull. The steering was very tight, i mean difficult to turn the wheel, as we turned around to run with the tide we could not get her to plane & only managed 10mph!
I took a few more pics but the boat will be dry on Friday when I can get better shots.

 

I would opt for the symmetrical bow shown in option 2. I would go as far forward with the hulls as practical to fit in with the line of the original hull. Then make the entries sharper than you have shown. Also take the entry of the bow of each hull a bit higher.

I would like to see some deadrise in the stern of the hulls but appreciate this would require more work. Without some lift in a turn there is a risk it will trip up and flip in a nasty fashion.

I prefer the outboard on the centreline but can see merit in the offset placement to get nice flow to the outboard.

What is the maximum length you feel would be sensible for the hulls? If you give me a number I will make a drawing of the hulls. Also what is the overall beam of the boat and spacing between the hulls?

Rick W.

 

Thanks Rick, I will take the shots & post the measurements on the weekend, cant wait to get going.

 

The boat is now in the yard, I have sort of decided to move the motor to the port hull. I know this is not ideal but feel we will have more chance of success & I am willing to compromise the looks & handling in exchange for performance. On that basis I have already cut away the transom & will be building a full length new one to facilitate the engines new posision.
I am all up for modding the bows but adding dead rise would be a lot more difficult, do you think simply adding a keel rail might help, ie - I could glass a piece of timber down the length & in the middle of the hulls?
Anyway the hulls are at present 3.7 long & I can add a further 750 to the length befor the reach the bow.

 

Don't add any keel.

The extra 750mm will be good.

What are the dimensions of the flat on each hull and the space between the flats?

Rick W

 

Rick, click on the last pic I have drawn the dimensions on the boat.

 

I attempted to draw what I think the hulls will look like - see attached. For simplicity the transom of the hulls is symmetrical.

Getting the bows to meet the aluminium hull might be interesting. I have guesstimated the shape.

These hulls reduce the depth of the trough by about 4". Likely to still be an issue for central mounted outboard. The ability to offset the outboard is certainly worth the effort.

Rick W.

 

OK thanks Rick I am on the case!
I will post a progress report soon.

 

I guess I might have just left the original hull alone and added akas and amas at gunwale level, then tied the top of a boarding ladder to one of the akas. Lines tied to the ladder's bottom would limit its submerged angle and lift it out of the water while underway. Philippine dive boats use this setup, it's simple and cheap and works great. They already have the akas and amas of course ...

Interesting mods you're making.

 

Here is my latest update - I have moved the motor to the starboard hull, I managed to use the existing steering & controls. I have not changed the hull shape.
Due to the circumstances, mid season & the cost of storing the boat in the yard I just wanted to get going, so the hull mods have been put on hold.
The result of moving the motor was quite dramatic! As the motor is new I have not revved it out but with 750 revs left to go she hits 34knt!
The point is she now works & in fact, works very well so far, very comfortable & stable traveling at 20kn.
Maybe over the winter I will rebuild the hull but to be honest I think a bigger cat is on the drawing board.
Thanks for all you help. Mart.