Sunday, April 22, 2012

"Fleet" launched

Fleet has had her launching day, and so far the performance report has been very satisfactory. Launching was said to have been as hectic as such occasions usually end up being, and the owner/builder thinks that at least thirty people had a go in the boat.

The engine used was a brand-new-out-of-the-box Suzuki 6hp four-stroke, and it was able to get the boat onto what felt like a plane with three heavy adults aboard. As there was no GPS available, accurate speeds were not recorded. As hoped, the ride was very smooth in a chop and through boat wakes, but there was no opportunity to get out into the ocean waves outside. What I find very satisfying is that the boat trimmed nicely when throttled back somewhat and remained dry throughout the tested speed range.

Tight turns at speed were stable and predictable.

Due to the business of the day, organised photography was not carried out, but here are a few snap shots. We plan to carry out more serious testing with 2.5hp, 4hp, 6hp, 9.8hp and oars.

A good view of the general proportions
Trim at rest with two adult men aboard
Running with the weight of two adults, under the urge of a new (and therefore tight) 6hp four-stroke Suzuki

Saturday, April 21, 2012

More photos of "Fleet", the planing version of "Flint"

The first example of Fleet, the planing hull version of Flint is getting much closer to launch day. In fact she has already been in the water to allow the marking of the waterline in preparation for the painting of the boot top - empirical data gathering!

Painting has gone ahead at a great rate, using the skills of people who normally apply coatings to aeroplanes and helicopters.

First real opportunity to view the hullform in the flesh.

 The hull shape is similar to the designs of the late William H. Hand, said to have been the inventor of the vee-bottomed motorboat. What made the William Hand designs significant was the way they would handle well at lower speeds when throttled back. Weston Farmer said of them, "They were steerable throughout their entire range of speed in following seas. The full planing boat is a dog in this department. Unless they are banging along full bore, you cannot steer them. And full bore in some seaways with this type of boat, demands Polident for the helmsman's teeth and metal brassiers for the ladies." ("From My Old Boat Shop" International Marine 1979.) Now, I think planing hull design has come some way since Weston Farmer formed his opinion, and there are some very fine designs around for full planing hulls, but the fact remains that for moderate planing and semi-planing speeds, a long, narrow Hand-style hull can be superb.

Getting ready for a trip down to the boat ramp for waterline marking. Gunwales are masked, as they will be finished bright using Deks Olje #1
First splash. Chines don't even touch the water when light. I hope that with a single oarsman on the forward thwart, the boat will be reasonably pleasant to row, even though she is a planing hull. Trim will be everything with passengers aboard.
25 litres of water in the aft well to represent the outboard and fuel, plus two people. The fellow on the helmsman's thwart is quite light, but the trim is very close to that predicted on the plans.
After the floatation tests, marks were made to allow masking-off for the boot-top.

Note the chinagraph pencil marks at the base of the stem.
Boot top masked ready for topside painting
Here you can visualise the fine, sharp lines up for'ard - she should give a smooth ride at moderate speed in a chop.
Almost ready for the water - just the oiling of the gunwales and breakwater/coaming to go. Test motor will most likely be a 6HP 4-stroke, but that is to be confirmed.

Thursday, April 19, 2012

Update on Low-powered planing hull "Fleet"

Since my last posting about Fleet, the planing version of my row/sail boat, Flint the owner/builder has been burning the midnight oil to get her finished. Here are a few photos to show progress, with a performance report to come in about three days time. The painting is proceeding rapidly, being done in an aircraft component spray booth!

Hull sanded, chines rounded-over, and 200gsm/6oz glass cloth being draped
Glass/epoxy sheathing. Given the work that was done on the bottom panel (see previous post) the cloth has been doubled in the forward sections of the bottom of the hull.
Glassing completed, and hull surface sanded. 12mm/1/2" gunwales have been added.
Spaced inwales being dry-fitted
The spaced inwales are of quite generous section on this particular boat, as the owner/builder will be using her in surf and unprotected waters on the Australian east coast for serious fishing. There are a number of other ways the topsides could be terminated, including side decks or simple laminated gunwales on the external surface only.
Being moved from the building location to the paint booth. The first opportunity to see her from a distance.
View of the interior showing some of the generous emergency buoyancy compartments. The large rectangular hatchs are non-standard, and are being used by this owner (who is a very experienced oceanic fisherman) for fishing equipment
First view of her profile
Coaming/breakwater and toe-rails added
In the paint shop - will be completed in about another 24 hours.
As I mention previously, I believe that there is a genuine need for small powerboats which have been optimised for operation under the urge of very small outboards. I nervously await the performance report from the first outing, which will be within the next three days. This example with be pushed by a 5hp Mercury, and has been built a little heavier than initially planned due to the rugged duties expected of her. A very light version, built in a manner similar to Flint, should go well with 2-1/2 to 4hp.

Wednesday, April 4, 2012

Low-powered planing hull - lessons learnt

Just before leaving on our recent road trip (4,500km), I wrote a post about a planing hull version of my popular Flint design. I was quite excited about the concept of a planing skiff for low-powered outboard, having had it in the back of my mind for a very long time.

With this latest design, (see here for details in the previous post), I had to produce the basic drawings in a very short space of time (about three days), as we were about to leave on what turned out to be more than four weeks of road travel. Having given thought to such a design in the past, I felt that I could get enough detail out to satisfy the owner/builder, who is an exceptionally capable person with high-level engineering qualifications.

Stitching-up Flint on which the new design is based
Here you can see the complex shapes which can be formed in plywood, as long as the panel shapes are "developable".
In order to produce a design which can be built stitch-and-glue from pre-computed plywood panels, one has to resort to relatively complex geometrical drawing. In the past, the drafting methods used to develop the panels tended to result in hulls which were full up for'ard and had straight buttock lines aft. The hulls so drawn are frequently apple-cheeked at the bow and lack displacement aft - not a good shape.

With the availability of complex hull modelling software, it is quite practical these days to engage in the design of developable hulls which were never possible in the past because of the unbelievable volume of calculation required in manual drafting. I am not a computer person, but I love my hull modelling and CAD software!

In my extreme rush to get drawings to the builder before leaving on our trip, I burnt the midnight oil fairing-up the hull shape on the computer, and when all was satisfactory, I hit the button to produce the panel developments.

Panel developments for one of my other designs
Off I went on four weeks of road travel, confident that the information provided would be adequate for my talented customer. The trouble is that in my confident state-of-mind I had neglected to test the developments as I usually do, using a scale model.

Scale model panel developments for Three Brothers, cut from 1/16" plywood

Testing panel developments at small scale
On the day of my return from the first of two long road trips conducted over the last four weeks, I received an email from my customer to say that he had cut all the panels for the planing hull version of of Flint (named Fleet) using his own CNC equipment (!), and that he was having problems with the initial stitching process. He was of the opinion that he was doing something wrong, having never built a stitch-and-glue boat, but I had a more sinister suspicion!

For a long time, I've had a feeling that some hull modelling programs have a hard time doing developments which incorporate large amounts of twist and bend at the same time. When one considers the unbelievable number of calculations required, and the geometrical complication, it is little wonder. In order to test my supposition, I reverse-engineered the offsets of Fleet into Gregg Carlson's "Hull Designer" program, which had proven itself to be very accurate at this sort of job in the past.

I generated a set of developments using the Carlson Hull Designer, and superimposed them over the ones I had generated from the other program. In the illustration below, you can see the Carlson developments in red, overlying the others in a dark colour. The topside panels are virtually identical, but the bottom panels show substantial difference.

Fleet developments showing the originals in black, and the Carlson Hull Designer developments in red.
As you can see, there was enough difference between the two different bottom panel developments to produce serious problems. So, my customer had not caused the problem - it was caused by my over-confidence, haste, and lack of testing! Below are some photos showing the result...

Bottom panel having failed in tension at the keel-line near the first frame (near the bow)
View of the failure from the inside. See how the crack has initiated at the keel line, and extended upwards and outwards from the keel line.
Having wiped the egg from my face, and being confident that the new developments would solve the problem in subsequent boats (but I will be doing tests this time!), the problem remained about how to fix the first boat without having to scrap the entire pair of bottom panels. The suggestion I made was along the lines of, "if you can't beat them, join them". I recommended to the customer (luckily for me he is a very clever and resourseful chap) that he use a saw to cut a whole series of of similar "failures" across the keel line both forward and aft of the initial failure, so that the topside panels could pull the incorrectly shaped bottom panels into the proper position. This was done, and with each successive cut the original failure closed up a little more, and an even bend formed in the keel line.

Here you can see some of the deliberately cut lines, filled with thickened epoxy and finished off with a "stop drill" at the upper end.The dark line closest to the camera is a scarph joint, but you can see the artificial "failure" cuts filled with white thickened epoxy forward of the scarph.
Glass tapes dry-fitted, with some extra tapes to reinforce the new cuts 
A wider view, showing how the repair has restored the boat to a nice, fair shape.
There are a number of lessons from this project: -
  • I should not assume that drawings for a new design are correct without testing them;
  • Never give up, because just about anything can be fixed if you do some careful thinking;
  • Don't take what I say too seriously, as I've proved myself to be wrong on frequent occasions!!!
Boat building  and designing is a lot of fun, and I really look forward to seeing how this particular boat turns out. I believe that there is a genuine need for an outboard-powered skiff which can perform well with a low-powered motor - say 4hp - and still be spirited and lively.