Wednesday, May 23, 2012

Answers to a couple of recent comments

Here is comment received regarding Fleet:-

How much does she weigh?
What I like about flint is that the center of balance is over the center thwart making her easy to carry and light enough for this senior citizen to car top.

Well, I can't tell you how much she weighs because we haven't weighed her yet, but the material thickness is the same as on Flint and the area of plywood is only 8.4% higher, indicating an 8.4% weight increase.  The Fleet shown in the pictures has a foredeck and inwales, but the standard Flint and Fleet have tank-tops on the foreward and aft buoyancy tanks, so it probably all evens out.

Based on just the plywood in the bare hull, the weight of Flint panels is 24kg(53lbs) and in Fleet the same is 26kg(57lbs). The centre-of-gravity of the hull panels (including transom without framing) is at 1.96metres forward of the aft perpendicular i.e. at the midships thwart near the aft edge.

The weight of any boat depends tremendously on the density of the materials used, and the attitude of the builder.
In relation to my recent post on the virtues of the sprit rig with the jib set flying, Dennis Marshall writes: -

May I ask what the line is hanging from the peak of the sail?

Dennis is asking about the light line which can be seen in a number of photos, running down from the head of the sail at the peak end of the sprit

The light line is just visible in this photo
The line is a vang. I suggested that it be used in certain conditions when hard on the wind and when running free, to control the amount of twist in the sail, and (when running) to prevent the head of the sail from moving forward of the beam i.e. forward of a a line drawn at right angles to the centreline of the boat. If a sail moves forward of the beam, it is a sure invitation to a 'Death Roll'.

The light line is run from the head of the sail near the peak of the sprit down to a thumb-cleat on the weather quarter and then to a little fairlead on the rudder head and then along the tiller to a small V-jamb cleat within easy reach of the helmsperson. When tacking or jibing, the line is flicked off the thumb-cleat and quickly moved to the one on the new weather quarter.  It only requires a light tension on the line (vang) to haul the head of the sail in to reduce twist in the sail.

Tuesday, May 22, 2012

Spritsail with Jib Set Flying

When I posted about the Sailing Pilot Boat-inspired design that I have started for Geoff Leedham, I was reminded about how much I like the Spritsail rig with a jib set flying.

Bertil Andersson's drawing of Lotsbat Skum
Back in about 1998, I think, I was working over what I thought would be the optimum-sized boat for solo and two-up beach-cruising ( see post here). The whole process became an obsession, and one of the things that I worked over in minute detail was the choice of rig. Over many decades I had sailed my existing boat with a range of different rigs, and had gathered a worthwhile amount of general daysailing and cruising experience using un-conventional rigs.

After much head-scratching, I settled on the spritsail with a flying jib (i.e. a headsail not hanked onto a stay), having been influenced by the writing of a number of people, of whom Phil Bolger was the most influential.

Why the spritsail? Here are my reasons: -
  • I wanted the shortest practical spars, and in particular, I want to be able to store the spars inside the boat. Several reputable authorities had written that the spritsail sets the maximum sail area on the minimum length mast;
  • A jib or staysail would be nice when sailing to windward - particularly a flying jib on an un-stayed mast;
  • The rigging needed to be very simple, and preferably easy to make and repair by hand using wood and line;
  • It was important to me that the centre-of-areas in the sail-plan be as low as possible to reduce the heeling moment;
  • The possibility of using the mainsail as a boomless sail as well as being usable with aboom was desirable. In really tough conditions, a boomless sail is a safety feature, as there is no boom to trip during a knockdown - you can alway ease a boomless sail but not so a boomed one;
  • A spritsail can be brailed if properly set-up.
The above list made lots of sense to me, but the overwhelming advantage seemed to be that the spritsail is one of the very few rigs which can carry a jib without any shrouds or back-stays. Any headsail needs plenty of tension in the luff or else it will sag off to leeward, drastically damaging windward performance. Usually the rig with a headsail of any sort needs shrouds with plenty of drift, and/or backstays in order to keep the luff taught.  A friend of mine who sails a Bolger Folding Schooner finds that it is necessary to drop his jib when going to windward, because the boat goes faster without it! This is because there are no stays and the jib sags badly when on the wind.

In the case of the spritsail, the sprit is placed under considerable compression by the snotter at the lower end (the heel end of the sprit). This compression is required to hold the head of the mainsail up and out and to keep the head of the mainsail taut.

Here you can see how the sprit pushes the head of the mainsail upwards and outwards
The above photo illustrates how the sprit tensions the head of the mainsail. The tension in the head of the sail is transmitted to the masthead, where it pulls aft strongly (somewhat like stays) and that, in turn, puts tension in the luff of the jib. A wonderful side effect is that as the wind gets stronger, the tension in the head of the sail gets greater, with the result that the tension in the luff of the jib increases just when it is needed - all in a rig which can be made by hand from a few bits of wood and some line!

Phoenix III getting to windward in fresh conditions with the jib standing very well, despite the lack of stays. In most other free-standing rigs the luff of the jib would be sagging badly.
Here is the same boat in even windier conditions, with a reef in the mainsail. Despite the reefed main and the blustery wind, the jib is standing very well once again. Note how the sprit snotter has been stretched by the stong wind and consequent high tension on the snotter - the crease from throat to clew highlights the problem - but the jib is fine.
In the photo above, the winds are lighter, but the boat is being sailed without the jib. Despite the lighter winds, the head of the mast is bending aft because there is no jib providing support. The mast bend has reduced head tension in the mainsail, allowing the unwanted throat to clew crease to form. Phoenix III was designed to balance well with or without the jib. Note how the tiller is pretty much centred, indicating that there is very little weatherhelm despite having only the mainsail set.

No rig is perfect, but the sprit rig offers simplicity, drive, low centre-of-area, short spars, and the ability to set a jib effectively without any stays. Perhaps the Scandinavians, Melanesians, Chinese, Dorymen, and Thames Bargemen, to name just a few, were several steps ahead of us...

Friday, May 18, 2012

Fleet - Some Initial Test Reports

Since my last post about Fleet, she has been used frequently and hard. Here is part of the text from some stuff I've posted on the Woodenboat Forum in response to questioning: -

This rig is light-weight - even with the relatively heavy 6hp 4-stroke

Firstly the missing dimensions: - LOA 15'/4572mm; breadth 4' 0-9/16"/1233mm; draft as drawn 4-3/4"/120mm; displacement 543-1/2 lbs/247kg. Hull is stitch-and-glue from 1/4"/6mm plywood panels, sheathed in 6oz/200gsm glass.

Testing so far has been with one, two, and three adults (and various combinations of children) using a 6hp Suzuki 4-stroke outboard which weighs 57lbs/26kg - the motor is brand-new and therefore tight, and no propeller development has been attempted. In relatively rough beach conditions (an open ocean exposed surf beach on the Australian east coast) with two large men aboard weighing 385lbs/175kg plus motor, and sundry equipment including water, the GPS-measured speed varied between 10 knots and 12 knots depending on trim and point-of-sail so to speak. The boat has been taken out through dumping surf, and back in again to the same beach, running straight up the beach at wave speed- this has been done repeatedly after fishing trips in the early hours of the morning.

On the day of the initial launching the boat was able to plane with three men aboard, although nobody had a GPS so the speed was not recorded. Now the speed may technically have been in the semi-displacement range, but the boat felt as though she was planing, and operated very nicely.

She has also been tried using a 2.5hp Suzuki 4-stroke and ran in a pleasant and surprisingly fast semi-displacement mode (two men and one man aboard). So far we haven't been able to record GPS speeds with the 2.5hp motor. As far as I'm concerned, the ultimate motor is a 4hp, because it is the largest motor we can use in this State without registration.

Limited rowing has been attempted, but results so far are encouraging. Here is a quote out of an email (unsolicited) from a very experienced tester: -
Hi Ross, yes I went East in Will's lightweight boat, your "Fleet" (called "San Pedro" ) this am.
Bit of a dump of waves on the beach at Moffat, but patience was rewarded by a nice clear push off the beach and a responsive (she shot away) row by the "old man" took us out quickly as the first couple of pulls on the motor failed to fire.
Quite a good ground swell, but lovely conditions on the surface with very light winds.

We motored around trialling the "new 6hp" for quite a while, and on two way runs found about a steady average 10 knots. (two up, (170kg plus say 15kg of gear). We did go to 12 with some wave assist. The waves go faster than the boat of course, which I believe adds to its safety as the fine entry would induce broaching at speed, a vice to be avoided in a light outfit.

Minor adjustments to trim (passenger facing forward and not back) lifted the speed by 10%.

A much nicer feel under way than a "tinny", of that there is no doubt.
I must say Ross, I was impressed beyond expectations as she really moved considering the load and was soft riding and quiet. I guess one of the benefits of the low power is that you can't get airborne, but you sure cover a lot of ground at 10 Knots. The boat with its glass skin and inhales and gunwales, seemed very strong and inspired confidence. I reckon she would be a fairly wet of course if choppy and the wind is off to the quarter. She will benefit from some attention to that aspect. (I know you already have the solution in mind.)
As a bonus on four short drifts away from Bray's reef, we kept four very respectable fish. (One squire and three sweeties, the biggest being over 1.5 Kg.)
Our return to the beach was fun with the good swell still running. We again just picked the time and Will. followed a good wave (with a gap behind it) and went smoothly (at 10 knots) up onto the beach. We jumped out and started pulling, one on each side and she went up the sand like she was on grease. (This is noteworthy as even a light "tinny" binds to the wet sand and is a cow to move up a sloping beach)Will put the dolly wheels under her and we ( actually Will and friend Tim) walked her back up the ramp and then the path to the unit.
Total time to the house from leaving Bray's reef was 15 minutes exactly. Some sort of record for off the beach I reckon.
The boat is a winner Ross, and such an easy build, with practical, useful, outcomes. My guess on motors is 6 hp (maybe 2 stroke) for outside, and 2 to 4 for calm work would easily get hull speed with a load. The big hatches that Will put in are fantastic, and we had all sorts of stuff in them. I wouldn't have it any other way. All he needs now is a leeboard, tiller and a fan or crab claw sail, and the picture would be complete. (wink wink)Thought you'd like a report from an old seasoned observer of small powered beach boats.Good luck and kind regards John

I also had this to say on the forum: -

The owner has just been on the 'phone to me to say that he has been taking out a lot of experienced boat-fishermen up where he lives in Caloundra (north of Brisbane, Australia) and he says that they are overwhelmingly impressed with the boat in the tough beach conditions they get up there - serious surf! What Will said was that these guys have forgotten what it is like to go beach fishing with a light and (hopefully) capable boat like Fleet (San Pedro) because they have spent years using tinnies and 'glass boats with big motors, and have forgotten the joys of light wooden boats.

On the day that the Tuna you see in the boat were caught, Will picked up a friend by backing down to the shore in substantial surf using the little 2.5hp motor and keeping the bow to the waves. They then went out through the surf to the point where he had seen the fish, and both got a hook-up. He said that even though they were relatively small fish as Tuna go, the pair still pulled the boat through the water enough to make a noticable wake. He said that characteristic makes her a "soft" fishing boat. I'm no fisherman, but he says it is a very good feature. He bled and gilled the fish on the way back in, and bailed the blood before the beach.

A significant point is that his friend is a real estate agent, and had put out his signs before coming down to meet the boat at 7.30. They completed the whole fishing and cleaning operation and were at home just after nine. The real estate agent went home, showered and got to his first "open house" before the advertised time of ten o'clock! The point of that long story is that if they had been using a large boat with 300hp of outboard, that fishing trip would not have taken place. Small and wooden is beautiful!

I'll report more when we get GPS data when using the 2.5hp, and if we can get one, a 4hp.

Wednesday, May 2, 2012

Swedish Sailing Pilot Boat - Lotsbat Skum

Geoff Leedham is a teacher at St. Philip's College Alice Springs, here in Australia. Alice Springs is right in the centre of Australia, thousands and thousands of kilometres from any coastline, right out in the desert country. Yes, you have to have schools everywhere, but what makes Geoff unusual as a teacher is that in this arid and remote location he runs a boatbuilding program for high school students. Geoff's program involves at least four different designs (to my knowledge - there may be more) and exposes the participants to a range of differing construction methods and techniques - for this I commend him.

Geoff with some of his students. The beautiful boat they have built, and are displaying here, is an Iain Oughtred-designed John Dory
Imagine what sorts of problem-solving issues have been dealt with by the high school students who built this boat
Another view of the John Dory as she sits in the school foyer, displaying the complexity of work required from a young team - art, engineering, chemistry, arithmetic, manual arts, project management and housekeeping to name a few.
As you may have determined, Geoff Leedham is an enthusiast, and like all nautically afflicted people, he has his own dreams. Some months ago, Geoff approached me by email and 'phone, seeking help with a pet project. The design he wishes to build represents a Sailing Pilot Boat from around 1910, and Geoff has obtained basic historical drawings from Bertil Andersson in Sweden.

There are two problems: -
  • there is no table-of-offsets;
  • Geoff wants to build in glued lapstrake and therefore hopes to minimise reverse curvature in the hull to simplify construction.
With this in mind, and having spoken with the plans supplier, Geoff asked me whether I could produce a modified set of lines which avoid the use of reversed sectional curvature, supply a set of building offsets, and draw up a schedule of scantlings for the new construction method. And just to top it off he wanted a heart-shaped transom in place of the original wine-glass.

An outboard profile and plan view taken from Bertil Andersson's website. I'd like to show you the body plan so as to give some indication of the extreme reverse curvature, but I do not want to show material without permission. However, you can take it from me - this is a curvatious boat in the extreme!
Here are the principal dimensions courtesy of Bertil Andersson: -

20½ foot.Length 6190, width 1800 mm.From Kalmarsund. Build in 1910's by Pelle Fräsare in Kalmar, Småland. Completely in oak.

Wondering whether my friend Mr Leedham had handed me a poisoned chalice, I gave it my best shot, and here are the results: -

These are my lines incorporating many changes from the original boat (which I commend to you, with the suggestion that you purchase plans from Bertil Andersson). You can see that cross-sectional reverse curvature has been reduced greatly, particularly amidships and in the run, but that the profile and plan have remained in the spirit of the original. This will be a lighter boat, reflecting her changed construction method, but she retains the character of the original with minimal changes. 

The above renderings show the modified Skum at 6.197m x 1.836m x 0.525m draft ( 20' 4" x 6' 3" x 1' 8-1/2") at a displacedment of 1041kg (2,290 lbs)

Below is a youtube video showing a fibreglass replica of the same, or similar boat to the one in the original drawings, under sail.

In addition to the lines drawings and off-sets, I have supplied Geof Leedham with a fairly detailed scantlings schedule, which I may publish if there is interest, and if Geoff agrees. He has paid me some money, and I need to be sensible with what I publish in case he refuses to take me for a sail!

Isn't it amazing to see what comes from a scheme to build boats in the desert?