Location: Southern England Renato Levi Wrote three books on the subject of designing Powerboats.
Best book currently available on powerboat hydrodynamics is Hydrodynamics of High-Speed Marine Vehicles, by Odd M.
If you are working in Aluminum, go to ABS, Lloyd's, or ISO and get rules for construction of high-speed vessels. Jet boats are tricky, most major water-jet manufacturers have lots of data on what works, talk to the supplier. A phenomenon known as porpoising can occur if you are not caqrefull of what you are doing on the bottom, particurly in the 6' infront of the transom. Make the delta pad on the bottom nice and long, no-one says that the boat needs a 'keel', where the bottom sheets meet to form the vee. Look at other jet boat manufacturers and what they do, we spend many hours making sure we get it right so we can sell a safe and well performing product. As has been said the key is power to weight and planing area in both laden and light conditions.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. The type of hull determines what kind of propeller is required to move the boat through the water. This is presently the most common bottom design, offering good speed with a softer ride that depends on the angle of the vee (called deadrise) the radius or shape of the keep line and the use of strakes. Each manufacturer choose how many and how far back (towards the transom) to bring each strake in order to achieve the desired performance characteristics. These boats are vee bottom with some degree of added outside hull often most prodeminant near the bow. If planing hulls are more efficient why don't we use them for carrying cargo and save the fuel that is lost in using the current heavy displacement bulk carriers? The only time planing is more efficient than displacement is if you apply a length constraint. Location: Sweden A planing boat is inefficient compared to displacement boats when operating at displacement speeds. If you look at the transom, a planing boat needs to separate abruptly from the water flow or you will get a negative lift.
A displacement boat is on the other hand optimised to let go of the water as gently as possible to minimize turbulence.
As I understand it, the requirements for an efficient displacement boat and for planing are contradictive. Please correct me if I'm wrong and there is a planing boat that is also efficient at displacement speeds (compared to true displacement boats).
Hull Designer is a simple, interactive, visual 3-d hull design Windows program for modeling and developing panels for hard chine construction.
This tutorial is very usefull for designing your own boat and even for redesigning other boats according to their boat plans which you can find in the DIY Boat Plans for Boat Building guide. Be careful not to open the Hulls generated .dxf file – if you do that you’ll get a 2d line drawing, not the 3d segments.
Thanks to Rick Malagodi for providing this great tutorial and a wonderful boating page you can see here. Location: Burleson, TX Hull ID Needed Been keeping an eye out for a hull to restore. Location: Key West Merc Panga Hull Mold For Sale The Original Merc Panga From Mercury Marine 26 Ft Hull Mold With Stand And Center Console Also One Stringer Kit Set This Mold Is Wax And Ready.
In the first chapter he describes his first catamaran design, Naramatac (spell it backwards).
If Naramatac had been lightly built with more beam, it might have performed a better, but wetted surface area would still be an issue. Location: Palm Beach County Check out the G-Cat's they have symmetrical thin hulls. I will make some adjustments to the model with SWATH type foils and see how far I can get that deep vee out of the water and reduce drag. The merc sj175 does offer a reasonable amount of thrust, but the downside is that in their infinate wisdom, Mercury put the exhaust from the engine in the cavity between the hull and jet unit.
I tend to think of those that do as 'old school', and perhaps we should scrap the shuttle and fly the appollo missions again.
As in aerospace, the trailing edges create a vortex, much like the tips of a wing, only in water that usually means that air is bled off, if that air makes it to the intake the pump will cavitate causing loss of thrust.


The propellers on these boats run totally submerged and will generally be of lower pitch, when powered by an outboard or stern drive. With sufficent power, these boats rise to the water's surface and operate in a skimming or planning mode, supported primarily by the water's velocity pressure. Their design is distinguislhed from a design by having a broad transom that meets the bottom with a basically sharp corner. A greater use of strakes tends to make the boat run higher and flatter, but a little harder. It differs from the older catamaran bottom in that the inside corners ( between the bottom and the tunnel) are quiet sharp.
Top end performance is usually superior to a true vee bottom, but this generally comes with a rougher ride in choppy water and does not carry a load as well as a conventional vee. Please ignore my generalization; I know that at planing speeds a planing boat will also displace water, so there is no clearcut distinction.
At displacement speed there will be lots of turbulence bhind the transom caused by the flow separation, reducing efficiency. Go to any small boat sailing regatta and observe the likes of the Thistle class, Windmills, 420s, 470s, Lasers, and many many more. Even though it might only be of academic interest, I still don't understand how a boat can be optimised for displacement mode and planing mode at the same time. At your coordinates 15 kn should be an attractive speed as it will get you to many interesting places within a few hours.
By using it you are able to find Center of Boyancy, Center of Lateral Area, Length Waterline, and righting moment (pitched or heeled) among other calculations.
Harris concluded "At all times the abundance of wetted area due to her fine lines added greatly to the total resistance.
The G-Cat was once rated by Randy Smythe as a Cadillac ride when compared to other beach cats. As much as I would like to make a SWATH it would take a considerable increase in time and budget. As I remember, they are nigh impossible to get hold of (you may have to order directly if you can find the website) but they are well worth reading.
If you have a 'rocker' the boat will bounce around, or porpoise, if it has a hook it will bow steer badly, possibly causing the boat to spin in a turn. Look at not only straight line performance, but also where any vorticied will end up in a tight turn (if you terminate your strakes ahead of the intake), if the unit cavitates during a turn and you loose thruse, a real nice jet spin often occurs, sometimes at an inconvient moment!!! The propellers on these boats often are not fully submerged and thus need to provide holding ability as well as higher pitch and rake because of the higher top-end speeds.
It may have squarish corners (called square, sharp or hard chines) or rounded corners ( called round or soft chines).
It is characteristic of such dual regime boats to have long fairly flat runs that have a very small angle with respect to the resting waterline.
I also added a seat, pedaling station and retractable outriggers: This image shows the outriggers in the retracted position. You can also create patterns for stem, stern, bulkheads, up to 10 chines, and up to 8 frames for construction. Open the Crossroads generated .dxf file into your AutoCad and there you have the 3d version of your Hulls design. They are generally designed with a somewhat pointed or rounded stern as well as a pointed or rounded bow.
Generally speaking the angle must be less than 4 degrees or else planing performance will need excessive power. Weight i relation to planing area seems to be one of the keys to a compromise that is good enough. The purpose of the outriggers is to providemore stability when standing up or moving about the boat. Was planning on doing a CC, and still could, but thought the molded in side console might help with the ID.
The normal position when I am sitting in thepedal station, or sleeping is retracted as shown above. Compared to some other standard hulls tested on the same chop it handled very nicely,slicing through the waves. The ability to get the transom above the water at displacement speeds, while keeping the angle low, is largely dependant on total displacement of boat, crew, and gear.
The buoyant outrigger hulls in the retractedposition should also assist in up-righting the boat upon a capsize.


Getting on a plane is another story, I don't think this boat could do that without an immense amount of power.
If the boat were to capsize with the outriggers extended, the mechanism forretracting them should allow for underwater operation. I would envision a rope, pulleys and hand-cranktype of mechanism for extending and retracting the outriggers (like the mechanism used for sails). The rear compartment is water-tight when the door betweenthe rear compartment and the pedaling station is closed.
A disadvantage of using this configuration to sleep, is the inconvenience of having toopen the hatch to look out for ships through the bubble. If the boat is being operated with the canopy top open,it would be important to make sure that both hatches to the forward and rear compartments are closed and sealed,in the event of a capsize. It would be advantageous to be able to use the rounded top as head-room for crawling intothese compartments.
The advantage of this is the convenience of getting upduring a sleep to look through the bubble to look for traffic.
The disadvantageis that is the pedaling station is allowed to get wet when pedaling with the canopy top open, water would getinto the supplies and equipment in the rear. I think sleeping configuration A would work better because it would ensure that thesleeping area is always kept dry. Perhaps a second small bubble could be placed over the rear sleepingcompartment, or some small windows in the rounded top.This animation shows 2 ways in which the outriggers could extend andretract, along with how the canopy top would retract.
Operation of it could be ropes, pulleys and a hand crank.The animation shows how the mono outrigger swings into extended positionvia the swing arm. I would also want to be able to steer from the sleeping cabin to keep the bow pointed into the on-comming waves.
Once the vector (direction the traffic is going) is known, I could simply pedal my boat away from the vector in a perpendicular line. Just pedal your ass off heading due west, and see where you end up, don't waste energy and time correcting your heading for a specific destination. If youre going to spend 40-50,000 dollars and a few years of effort to be out there, I just think it makes sense to think a bit more about what you're going to get out of being there, not just about making it to the other side.
I would tend to make the outriggers fixed structures - less to go wrong, stronger and you wont have to worry about your canopy getting in the way - the drag will be neglegible . If none make sure they are up to the task and built simple and very strong - they will take a beating. Be mindfull of the volume of water that is likely to get into the hull - it will not be calm weather if this happens and you will need a means of getting this water out or stopping alot of it getting in. You could afford somne legal windage towards the bow to help keep her pointing down wind whilst asleep or resting - consider autohelm if you are carrying enough power - I am convinced for solo row thins device would not only save distance but if you were able to keep your boat pointed down wind this would also increase boat speed during down time. The Woodvale boats sometimes popped along at 2.5 to 3 knots by pointing them downwind with their natural windage. Calculate the right size of sea anchor for the weight and bouyancy of your craft - to small and its not worth having as it will not bring the craft perpinticular to the direction of the waves - too large and it may start dragging you under. If you get your sea anchor deep enough you may even find you are able to MAKE ground against the wind with it deployed - this happened to me at Cape Finisterre. Cooking is another thing to consider - force10 gimballed single burner stove is good and takes standard propane 500g propane- each gas bottle lasted me a week to ten days. This is probably stating the obvious again but the canopy should maybe flip backwards and up with some goretex or canvas sprayboards at the side -this will give a degree of protection to you in larger breaking following seas - again this needs to be very strong if it is your only means of keeping the water out. The canopy should also have some form of emergency release incase it jams - or you build another means of escape. Batteries in EPRIB's only last for 48 hours max - I would put 20, not 2 flares into your grab bag (the military have very good lightweight miniflares) and a mini hand pumped watermaker may weigh less that emergency water. It wouldn't hurt to have a few rope handgrips on the outside of the hull - you may need to get out and clean of razor barnicles in the last week or so. Antifouling, regrettfully, does not seem to keep these little critters off terribly effectively unless you have stronger stuff state side. This may give slightly higher speed numbers than I have given but my numbers are for smooth water and waves will help or hinder.



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