Slot Affect Sailing

• Converting a Rowing Dinghy to Sail

• Click on these to see them full size:

(A)

(H)

(T)

(F)

Cranks With Planks Present:

<> Converting a Rowing Dinghy to Sail <>

[First published in THE RUDDER in 1954, this gem is Blandford at his best. If you've never checked out his books you'll be amazed at his output over the years. Plans for his canoes and kayaks are still available, I'm told, from Clark-Craft. These include folding kayaks and canvas boats. -- COD]

MOST rowing dinghies are suitable for conversion to sail. The result will not be a racing boat, although she will be able to sail on all usual points and give her owner immense pleasure while he is using his skill to make the wind do the work. To convert a rowing dinghy to sail, besides the mast and sail with the attendant rigging, there must be some form of a keel to prevent leeway, and a rudder deeper than is needed merely for rowing. It is an advantage if the conversion can be done without affecting the suitability of the boat for rowing or for an outboard motor. It is also worth while to choose a rig which can be dismantled and stowed within the boat if necessary.

Most rowing dinghies are of comparatively shallow draft so that the addition of sail without increasing the keel surface will result in a craft capable of sailing downwind only, an attempt to sail in any other direction resulting in probably as much leeway as forward progress. The sail could be added first and the dinghy used providing its limitations are realized.

There are many possible rigs for a small boat. For a knockabout type of conversion the sail plan should consist of a single sail. If cost is to be kept low there should be a minimum number of fittings to buy. A sail which answers these requirements and is easily stowed is the balanced lug (A). The beginner is unlikely to come to any harm while sailing with this rig, yet he can carry out all the usual sailing maneuvers and use his boat to go places.

Of course there cannot be any universal sailing rig suitable for all dinghies, but most dinghies of the yacht tender type, whether round bottomed or hard chine or built with plywood or planked skin, conform to a general proportion and can be converted to sail with a good chance of success. The conversion described in this article is based on a common 10 foot dinghy. For other size boats the main dimensions can be altered proportionately. The sail size errs on the small side and will certainly not overcanvas an average rowing dinghy hull.

The mast, yard and boom are all 9 feet long. The mast should have a maximum diameter of about 2-1/2 inches and taper to about 1-1/2 inches at the top. Suitable woods are fir or spruce. It could be shaped up from square stock, but for this sort of craft it is simplest to use a natural pole with the bark stripped off. A natural pole may have a few lengthwise cracks or shakes, but they do not matter provided they are small. Clean up the pole with draw knife and plane and then sand. The thickest part should come near gunwale level.

In a 10 foot dinghy the mast is located about 18 inches back from the stem. It is unlikely that there will be a rowing thwart there and the simplest support for the mast is a board fixed across the gunwales. This may have a central hole for the mast (B), or if the boat will have to negotiate low bridges frequently there could be a U shaped notch with a metal keeper to swing across (C).

The foot of the mast should have a tenon cut in it to fit a block screwed to the hog [keelson] (D). Arrange this so that the mast stands upright.

The mast may be stiff enough to stand without stays, but it is more likely to need a forestay and a pair of shrouds. These are best made of steel wire, but they could be fiber rope. To support them fit two wooden chocks on each side of the top of the mast. Cut a slot below them for the sheave (E) which takes the halliard.

The shrouds may be in a continuous length, looped around the top of the mast and taken down to shroud plates (F) on each gunwale, about 6 inches aft of the mast. Rigging screws could be used, but for economy the old fashioned lanyards are satisfactory.

If the mast passes through a hole in its thwart the forestay may be arranged with a lanyard to a ring on the stem head in the same way as the shrouds. If the mast is arranged so that it may be lowered it is better for the forestay to be brought to a pair of blocks, with a halliard leading aft to a conveniently placed cleat (G).

The yard should be kept light. It is nine feet long and may be of fir or spruce, with a thickness of about 1-1/2 inches where the halliard is attached and tapering a little towards the ends (H). A bamboo pole of the same size may be substituted for solid wood.

Lightness is not needed in the boom. In fact a reasonable amount of weight is desirable. The boom may be solid wood about 1-1/2 inches in diameter, or a square with rounded corners makes a modern section. This is also 9 feet long. The only work on these two spars is to drill a 3/8 inch hole near each end.

It is best to have the sail (I) professionally made to the sizes given. If you make it yourself use a light grade sailcloth, reinforce the corners well, and rope all around if possible. In any case rope the short luff and 12 inches or so along the head and foot of the sail. Put cringles or substantial eyelets in each corner and a row of eyelets along the head. A row of reef points may be arranged about 15 inches up from the foot.

Fasten the corners of the sail to the yard and boom with light line, taken around the spars and through the holes. Do not stretch excessively or the set of a new sail will be spoiled. Fasten the head of the sail to the yard with marline hitching (J) through the eyelets. Fasten a short tack line to the forward end of the boom. After the sail is hoisted by the halliard the tack line is hauled back to a cleat on the side of the mast. The yard may have an eye attached to connect with a traveler on the mast (K).

A simpler arrangement is to merely tie the halliard to the yard, preferably using a topsail halliard bend (L). Experiment to get the best set. The yard should clear the forestay as it swings over. When the best set is found, mark the yard and fix the cleat for the tack line. Put a similar cleat on the other side to take the halliard. Alternatively the halliard may be taken through a small block and led aft to a cleat on a thwart so that it becomes possible to lower the sail without moving forward.

The sheet to control the sail (M) is eye spliced to the boom and led direct to the hand. There is no need for the complication of tackle to give extra purchase on this small sail.

[COD: Here I disagree with Blandford. Put a block on the boom. Knot both ends of the sheet.
[Your sheet should be long enough that, when the sail is 90 degrees to the centerline, you can hold the end comfortably, and then some. Next, put a block on the rudder head, or on a lanyard on either quarter (stern corner). Untie the knot in one end of the sheet and run it through the new block. Knot it. Now, when running before the wind you can let the sail out and the two knots stop you from ever losing the sheet. You grab it somewhere in the middle, depending on where you're sitting in the boat, to sheet the sail when running, or you can tug on the end passing through the stern block.

When heading upwind, you grab the knot at the boom end as the sail comes inboard, and sheet with that. The other knot stops at the stern block and you now have a 2:1 purchase. Even on such a small sail it's a lot more relaxing to have a sheet purchase. This is an old canoe-sailing trick. Of course, you can also pass on block #2, and put a carabiner or snap hook on one end of the sheet. The hook snaps onto a padeye, or sturdy loop of line, on the bottom of a thwart or on the bottom of the boat as in (T). You use the sheet the same way, but it's not 'double-ended'.]

If the boat already has a rudder its blade may be lengthened or a longer blade may be substituted depending on the design of the steering gear. If a rudder has to be made one with a hinged blade will be most convenient. The blade may be of aluminum alloy or galvanized steel, in which case it will stay down under its own weight, or it may be of wood and held down by rubber under tension. Make the stock of two pieces of 1/2 inch plywood separated by a piece slightly thicker than the blade (N). The stock should reach from just above the keel level to a few inches above the transom. Thicken the top and slot it to take the tiller (O).

The hangings may be regular gudgeons and pintles (P) or pieces of strip steel of about 1/4 by 1/8 inch section may be bent and screwed on so as to mate with a 1/4 inch rod hinge pin (Q).

If the blade is of metal it need not be more than 1/4 inch thick. If plywood is used it should be 1/2 inch. Pivot the blade on a bolt. With a wooden blade arrange a stop (R) so that the rubber does not pull the blade too far.

The simplest method of providing a grip on the water is by using a leeboard. This is not as good looking as some sort of a lifting keel, but it is simple and quite effective. Large craft which favor this method of providing keel surface are the Thames sailing barges and many Dutch coasters and sailing yachts. On large boats there are two boards, but only the one on the lee side is lowered. In a dinghy the board is light enough to be lifted over when going about. The board may be of plywood or solid wood, about 5/8 inch thick, large enough to project about 2 feet below the keel line; and about 8 inches wide (S).

Shape it to a streamlined section below the water. The simplest method of hanging the leeboard is by a rope from the bottom of the boat resting against a peg in a rowlock socket (T). The only objection to this is that it does not allow fore and aft adjustment and the main rowlock socket is likely to be too far aft for correctly balancing the underwater profile with the sail plan.

The more conventional way of adding keel surface is by building in a watertight casing to take a drop keel or centerboard. For a small dinghy the simplest arrangement and the one that takes up the least room in the boat is a daggerboard which pushes straight down its trunk instead of hinging up. The forward edge of the daggerboard should be about 2 feet aft of the mast.

The daggerboard may be made of marine plywood or solid wood, about 5/8 inch thick, or 1/4 inch metal as described for the rudder blade. The underwater part of a wooden daggerboard should be shaped and streamlined in the same way as a leeboard. The daggerboard trunk needs to be braced securely in the boat as there may be considerable sideways pressure on it when sailing with the wind abeam. Its arrangement will depend on the particular boat. Most craft built for rowing only do not have a keel wide enough to permit the cutting of a slot without weakening the cut members. In such a case it is better and simpler to have the daggerboard off center, passing through a slot in the skin to one side of the keel. This will not affect the performance of the boat. The trunk should be made so that its top comes above the waterline (U). If it comes level with the top of the thwarts that usually is high enough and is convenient for fitting.

Make the trunk with plenty of clearance around the daggerboard and shape it so that the board will have a slight rake aft. The box may be built of 5/8 inch plywood glued and screwed together, or slightly thicker solid wood may be used. If solid wood is used have the grain of all pieces going the same way so that any expansion or contraction is uniform and unlikely to strain the joints or cause cracks. Curve the bottom of the trunk to suit the skin and cut away any ribs or other structural members so that it will bed down properly.

Mark the position of the slot on the skin and cut it out by drilling holes at each end and sawing between them. Leave the final trimming to size until the trunk [missing line] under way it is advisable to use a wood glue which sets hard. It is better to bed the trunk down on a piece of canvas liberally coated with one of the flexible stopping compositions which never sets hard. Screw the parts from below.

How the top of the trunk is fitted will depend on its relation to thwarts and other parts. It may get sufficient support by being notched into a thwart or a gangplank may be fitted between two thwarts (V). Build up the top of the daggerboard (W). A metal board will stay down under its own weight. There are two ways of fitting a wooden board so that it will stay down under normal circumstances, but will rise if it hits an obstruction. A rubber strap may be hooked over the top (X) or friction can be provided inside the trunk by rubber nailed on each side of the board (Y).

If the dinghy also is towed behind a power boat or driven by an outboard motor it may be worth while making a plug to fit the top of the trunk when the daggerboard is removed, otherwise water may be forced up the trunk at speed and give you wet pants or some unnecessary bailing.

The various sizes mentioned should give satisfactory sailing with an average dinghy. In the first trials under sail experiment with various positions for attaching the halliard to the yard and with various degrees of tension on the tack line. Your position in the boat also will have considerable effect on her sailing performance. With the wind aft you may be near the stern, but as the wind comes abeam or forward of it you probably will get the best results by sitting near amidships.

• Converting a Rowing Dinghy to Sail

• Click on these to see them full size:

(A)

(H)

(T)

(F)

Cranks With Planks Present:

<> Converting a Rowing Dinghy to Sail <>

[First published in THE RUDDER in 1954, this gem is Blandford at his best. If you've never checked out his books you'll be amazed at his output over the years. Plans for his canoes and kayaks are still available, I'm told, from Clark-Craft. These include folding kayaks and canvas boats. -- COD]

MOST rowing dinghies are suitable for conversion to sail. The result will not be a racing boat, although she will be able to sail on all usual points and give her owner immense pleasure while he is using his skill to make the wind do the work. To convert a rowing dinghy to sail, besides the mast and sail with the attendant rigging, there must be some form of a keel to prevent leeway, and a rudder deeper than is needed merely for rowing. It is an advantage if the conversion can be done without affecting the suitability of the boat for rowing or for an outboard motor. It is also worth while to choose a rig which can be dismantled and stowed within the boat if necessary.

Most rowing dinghies are of comparatively shallow draft so that the addition of sail without increasing the keel surface will result in a craft capable of sailing downwind only, an attempt to sail in any other direction resulting in probably as much leeway as forward progress. The sail could be added first and the dinghy used providing its limitations are realized.

There are many possible rigs for a small boat. For a knockabout type of conversion the sail plan should consist of a single sail. If cost is to be kept low there should be a minimum number of fittings to buy. A sail which answers these requirements and is easily stowed is the balanced lug (A). The beginner is unlikely to come to any harm while sailing with this rig, yet he can carry out all the usual sailing maneuvers and use his boat to go places.

Of course there cannot be any universal sailing rig suitable for all dinghies, but most dinghies of the yacht tender type, whether round bottomed or hard chine or built with plywood or planked skin, conform to a general proportion and can be converted to sail with a good chance of success. The conversion described in this article is based on a common 10 foot dinghy. For other size boats the main dimensions can be altered proportionately. The sail size errs on the small side and will certainly not overcanvas an average rowing dinghy hull.

The mast, yard and boom are all 9 feet long. The mast should have a maximum diameter of about 2-1/2 inches and taper to about 1-1/2 inches at the top. Suitable woods are fir or spruce. It could be shaped up from square stock, but for this sort of craft it is simplest to use a natural pole with the bark stripped off. A natural pole may have a few lengthwise cracks or shakes, but they do not matter provided they are small. Clean up the pole with draw knife and plane and then sand. The thickest part should come near gunwale level.

In a 10 foot dinghy the mast is located about 18 inches back from the stem. It is unlikely that there will be a rowing thwart there and the simplest support for the mast is a board fixed across the gunwales. This may have a central hole for the mast (B), or if the boat will have to negotiate low bridges frequently there could be a U shaped notch with a metal keeper to swing across (C).

The foot of the mast should have a tenon cut in it to fit a block screwed to the hog [keelson] (D). Arrange this so that the mast stands upright.

The mast may be stiff enough to stand without stays, but it is more likely to need a forestay and a pair of shrouds. These are best made of steel wire, but they could be fiber rope. To support them fit two wooden chocks on each side of the top of the mast. Cut a slot below them for the sheave (E) which takes the halliard.

The shrouds may be in a continuous length, looped around the top of the mast and taken down to shroud plates (F) on each gunwale, about 6 inches aft of the mast. Rigging screws could be used, but for economy the old fashioned lanyards are satisfactory.

If the mast passes through a hole in its thwart the forestay may be arranged with a lanyard to a ring on the stem head in the same way as the shrouds. If the mast is arranged so that it may be lowered it is better for the forestay to be brought to a pair of blocks, with a halliard leading aft to a conveniently placed cleat (G).

The yard should be kept light. It is nine feet long and may be of fir or spruce, with a thickness of about 1-1/2 inches where the halliard is attached and tapering a little towards the ends (H). A bamboo pole of the same size may be substituted for solid wood.

Lightness is not needed in the boom. In fact a reasonable amount of weight is desirable. The boom may be solid wood about 1-1/2 inches in diameter, or a square with rounded corners makes a modern section. This is also 9 feet long. The only work on these two spars is to drill a 3/8 inch hole near each end.

It is best to have the sail (I) professionally made to the sizes given. If you make it yourself use a light grade sailcloth, reinforce the corners well, and rope all around if possible. In any case rope the short luff and 12 inches or so along the head and foot of the sail. Put cringles or substantial eyelets in each corner and a row of eyelets along the head. A row of reef points may be arranged about 15 inches up from the foot.

Fasten the corners of the sail to the yard and boom with light line, taken around the spars and through the holes. Do not stretch excessively or the set of a new sail will be spoiled. Fasten the head of the sail to the yard with marline hitching (J) through the eyelets. Fasten a short tack line to the forward end of the boom. After the sail is hoisted by the halliard the tack line is hauled back to a cleat on the side of the mast. The yard may have an eye attached to connect with a traveler on the mast (K).

A simpler arrangement is to merely tie the halliard to the yard, preferably using a topsail halliard bend (L). Experiment to get the best set. The yard should clear the forestay as it swings over. When the best set is found, mark the yard and fix the cleat for the tack line. Put a similar cleat on the other side to take the halliard. Alternatively the halliard may be taken through a small block and led aft to a cleat on a thwart so that it becomes possible to lower the sail without moving forward.

The sheet to control the sail (M) is eye spliced to the boom and led direct to the hand. There is no need for the complication of tackle to give extra purchase on this small sail.

[COD: Here I disagree with Blandford. Put a block on the boom. Knot both ends of the sheet.
[Your sheet should be long enough that, when the sail is 90 degrees to the centerline, you can hold the end comfortably, and then some. Next, put a block on the rudder head, or on a lanyard on either quarter (stern corner). Untie the knot in one end of the sheet and run it through the new block. Knot it. Now, when running before the wind you can let the sail out and the two knots stop you from ever losing the sheet. You grab it somewhere in the middle, depending on where you're sitting in the boat, to sheet the sail when running, or you can tug on the end passing through the stern block.

When heading upwind, you grab the knot at the boom end as the sail comes inboard, and sheet with that. The other knot stops at the stern block and you now have a 2:1 purchase. Even on such a small sail it's a lot more relaxing to have a sheet purchase. This is an old canoe-sailing trick. Of course, you can also pass on block #2, and put a carabiner or snap hook on one end of the sheet. The hook snaps onto a padeye, or sturdy loop of line, on the bottom of a thwart or on the bottom of the boat as in (T). You use the sheet the same way, but it's not 'double-ended'.]

If the boat already has a rudder its blade may be lengthened or a longer blade may be substituted depending on the design of the steering gear. If a rudder has to be made one with a hinged blade will be most convenient. The blade may be of aluminum alloy or galvanized steel, in which case it will stay down under its own weight, or it may be of wood and held down by rubber under tension. Make the stock of two pieces of 1/2 inch plywood separated by a piece slightly thicker than the blade (N). The stock should reach from just above the keel level to a few inches above the transom. Thicken the top and slot it to take the tiller (O).

The hangings may be regular gudgeons and pintles (P) or pieces of strip steel of about 1/4 by 1/8 inch section may be bent and screwed on so as to mate with a 1/4 inch rod hinge pin (Q).

If the blade is of metal it need not be more than 1/4 inch thick. If plywood is used it should be 1/2 inch. Pivot the blade on a bolt. With a wooden blade arrange a stop (R) so that the rubber does not pull the blade too far.

The simplest method of providing a grip on the water is by using a leeboard. This is not as good looking as some sort of a lifting keel, but it is simple and quite effective. Large craft which favor this method of providing keel surface are the Thames sailing barges and many Dutch coasters and sailing yachts. On large boats there are two boards, but only the one on the lee side is lowered. In a dinghy the board is light enough to be lifted over when going about. The board may be of plywood or solid wood, about 5/8 inch thick, large enough to project about 2 feet below the keel line; and about 8 inches wide (S).

Shape it to a streamlined section below the water. The simplest method of hanging the leeboard is by a rope from the bottom of the boat resting against a peg in a rowlock socket (T). The only objection to this is that it does not allow fore and aft adjustment and the main rowlock socket is likely to be too far aft for correctly balancing the underwater profile with the sail plan.

The more conventional way of adding keel surface is by building in a watertight casing to take a drop keel or centerboard. For a small dinghy the simplest arrangement and the one that takes up the least room in the boat is a daggerboard which pushes straight down its trunk instead of hinging up. The forward edge of the daggerboard should be about 2 feet aft of the mast.

The daggerboard may be made of marine plywood or solid wood, about 5/8 inch thick, or 1/4 inch metal as described for the rudder blade. The underwater part of a wooden daggerboard should be shaped and streamlined in the same way as a leeboard. The daggerboard trunk needs to be braced securely in the boat as there may be considerable sideways pressure on it when sailing with the wind abeam. Its arrangement will depend on the particular boat. Most craft built for rowing only do not have a keel wide enough to permit the cutting of a slot without weakening the cut members. In such a case it is better and simpler to have the daggerboard off center, passing through a slot in the skin to one side of the keel. This will not affect the performance of the boat. The trunk should be made so that its top comes above the waterline (U). If it comes level with the top of the thwarts that usually is high enough and is convenient for fitting.

Make the trunk with plenty of clearance around the daggerboard and shape it so that the board will have a slight rake aft. The box may be built of 5/8 inch plywood glued and screwed together, or slightly thicker solid wood may be used. If solid wood is used have the grain of all pieces going the same way so that any expansion or contraction is uniform and unlikely to strain the joints or cause cracks. Curve the bottom of the trunk to suit the skin and cut away any ribs or other structural members so that it will bed down properly.

Mark the position of the slot on the skin and cut it out by drilling holes at each end and sawing between them. Leave the final trimming to size until the trunk [missing line] under way it is advisable to use a wood glue which sets hard. It is better to bed the trunk down on a piece of canvas liberally coated with one of the flexible stopping compositions which never sets hard. Screw the parts from below.

How the top of the trunk is fitted will depend on its relation to thwarts and other parts. It may get sufficient support by being notched into a thwart or a gangplank may be fitted between two thwarts (V). Build up the top of the daggerboard (W). A metal board will stay down under its own weight. There are two ways of fitting a wooden board so that it will stay down under normal circumstances, but will rise if it hits an obstruction. A rubber strap may be hooked over the top (X) or friction can be provided inside the trunk by rubber nailed on each side of the board (Y).

If the dinghy also is towed behind a power boat or driven by an outboard motor it may be worth while making a plug to fit the top of the trunk when the daggerboard is removed, otherwise water may be forced up the trunk at speed and give you wet pants or some unnecessary bailing.

The various sizes mentioned should give satisfactory sailing with an average dinghy. In the first trials under sail experiment with various positions for attaching the halliard to the yard and with various degrees of tension on the tack line. Your position in the boat also will have considerable effect on her sailing performance. With the wind aft you may be near the stern, but as the wind comes abeam or forward of it you probably will get the best results by sitting near amidships.