A couple of notes on my approach to this before we begin the main design specs.

1. I'm assuming the coating only repels free water, not the water in the bodies of the people in the boat.

2. A mass of water equal to the mass of the vessel will be displaced from below the vessel. Whether the vessel is in contact with the water or not doesn't change this. In practice exactly the same rules of buoyancy apply as to a normal boat, if you fail to displace sufficient volume of water for the mass of your vessel, it will still sink. It will sink in a little bubble of repelled water, but it will sink.

Start with a dragonboat, they're beautifully designed fast boats which take a lot of people. We're going to run this like a normal boat, hull in the water. Lightly coat the gunwales and inside of the hull with your hydrophobic substance. The most important factor in any boat is keeping the people inside and the water outside, this use of your magic coating will serve particularly well for this. No need to worry about waves washing over the side or enemies squirting water at you risking swamping or sinking your boat. It'll also make it significantly more comfortable inside for your (dry) paddlers.

Add outriggers, these are going to make full use of your magic coating. Full length, wide enough for a warrior to stand on and fully coated in your magic substance. These are going to act both for stability and as a fighting/hunting platform. They'll have a stabilising effect significantly greater than their mass and volume would normally allow for.

Your magic substance is used for stability, improved versatility and comfort, but not as a critical element. Controlling a boat is already a fine art, having the hull in the water makes the boat controllable, whether you choose to sail it, row it, or paddle it like a big canoe, boat control is about balance of forces. Once you start taking some of those forces out of the system you get an unbalanced equation and control becomes particularly difficult.

Hull design isn't a simple game, whether you choose hard or soft chines, a "V" hull or flat bottom, carvel or clinker, daggerboard, centreboard or leeboard, fixed keel or lift keel, bilge keel or wing keel, all these things are significant, in most cases they're not compromises but deliberate design decisions fundamentally changing the boat for different purposes. If you fully coat the hull in your substance you take away all these options and leave yourself with at best a vague shapeless hull. Keep the boat in the water.

A couple of notes on my approach to this before we begin the main design specs.

1. I'm assuming the coating only repels free water, not the water in the bodies of the people in the boat.

2. A mass of water equal to the mass of the vessel will be displaced from below the vessel. Whether the vessel is in contact with the water or not doesn't change this. In practice exactly the same rules of buoyancy apply as to a normal boat, if you fail to displace sufficient volume of water for the mass of your vessel, it will still sink. It will sink in a little bubble of repelled water, but it will sink.

Start with a dragonboat, they're beautifully designed fast boats which take a lot of people. We're going to run this like a normal boat, hull in the water. Lightly coat the gunwales and inside of the hull with your hydrophobic substance. The most important factor in any boat is keeping the people inside and the water outside, this use of your magic coating will serve particularly well for this. No need to worry about waves washing over the side or enemies squirting water at you risking swamping or sinking your boat. It'll also make it significantly more comfortable inside for your (dry) paddlers.

Add outriggers, these are going to make full use of your magic coating. Full length, wide enough for a warrior to stand on and fully coated in your magic substance. These are going to act both for stability and as a fighting/hunting platform. They'll have a stabilising effect significantly greater than their mass and volume would normally allow for. What's going to surprise you here is that the greatest risk is making the outriggers too buoyant. To a certain extent they need to be overwashed as they hit waves independently of the main hull, otherwise the forces on them transmit negatively back to the hull, making the whole thing a lot more uncomfortable than it needs to be along with risking high stresses on their struts and breaking the whole thing up.

Your magic substance is used for stability, improved versatility and comfort, but not as a critical element. Controlling a boat is already a fine art, having the hull in the water makes the boat controllable, whether you choose to sail it, row it, or paddle it like a big canoe, boat control is about balance of forces. Once you start taking some of those forces out of the system you get an unbalanced equation and control becomes particularly difficult.

Hull design isn't a simple game, whether you choose hard or soft chines, a "V" hull or flat bottom, carvel or clinker, daggerboard, centreboard or leeboard, fixed keel or lift keel, bilge keel or wing keel, all these things are significant, in most cases they're not compromises but deliberate design decisions fundamentally changing the boat for different purposes. If you fully coat the hull in your substance you take away all these options and leave yourself with at best a vague shapeless hull. Keep the boat in the water.