Ideas For My Dream Boat
Page 1 of 2

Author:  Fred [ Fri Oct 04, 2013 2:07 pm ]
Post subject:  Ideas For My Dream Boat

Today I stumbled upon a boat which is as close to perfect as I can imagine for her size. She's Kiwi designed and built (like the Oracle/USA boat :-p), but with American styling. There are a number of ideas in her that I love and would love to emulate one day along with some of my own. This thread will be locked, and this post will serve as an index to the following posts.

I guess my goals are something like this:

  • Comfortable for 4 to 8 people to exist on for a week or more without land contact.
  • Safe and relatively easy to operate for a lonely skipper when necessary.
  • Light enough to be affordable to run and to make good speed on minimal power.
  • Sufficient range and durability to consider doing international trips.
  • Attractive to look at, from all angles.
  • Easy to keep clean and tidy during use.
  • Plenty of good living space inside.
  • Plenty of good working space outside.
  • Does not dig its arse in when going fast or fastish.
  • Good easy access to engine for maintenance and replacement.

As usual for me, only perfection will do. And that takes significant insight and planning to achieve. I've been dreaming this for years, it's time to jot some of it down. Ideally I'd eventually build a parametric model with constraints and allow a computer to design it for me. That's unlikely, though. I might instead build a real model and check my assumptions on that at 1:10 scale or so.

Structural discussion or perhaps monologue: viewtopic.php?f=13&t=2305

List of posts:


Author:  Fred [ Fri Oct 04, 2013 2:08 pm ]
Post subject:  Bow deck shape

Bow deck shape

Docking to a wharf is often a pain. If you're standing on the foredeck you can not reach the wharf. If you're standing on the side, you are not close to the forward most cleat that you need to be close to. This is accentuated by having a pointy bow. The boat that I just fell in love with has a ROUND bow, which tapers to a fine point at the water line. This does a few things. It improves the shape and look of the front 1/3 of the hull. It offers more deck space for working and storage. It potentially offers more strength from a single piece construction across the front. And it puts you closer to the wharf in the part of the boat you need to be in. Nice.

Author:  Fred [ Fri Oct 04, 2013 2:09 pm ]
Post subject:  Cockpit edges

Cockpit edges

There must be an undercut for your feet and support for your thighs at a good height! Without this, you're in danger of falling overboard, which is obviously bad, especially if alone at sea. Another good feature is to have the surface at a suitable height for working on while standing. I'd say 800 is the ideal height. Any higher and you can't operate a rod from your groin. Any lower and there is insufficient surface area to be comfortable with extreme pressure on your thighs. 100mm of height would be minimum, 200 maximum, but the lower edge can't extend below the knees, which in my case means 600. Additionally, it's VERY nice to be able to safely navigate this edge on foot without descending into the cockpit. For this you need width, 270 being the minimum, and more being better up to about 400 where it might start to look weird and ugly.

Author:  Fred [ Fri Oct 04, 2013 2:09 pm ]
Post subject:  Belting


A real boat MUST be able to impact a wooden/log wharf pile with significant force and sustain no damage. This is essential as it's regularly necessary to dock against a wharf with waves moving the boat. The highest risk is when initially docking, however the boat can and will move with the waves while docked, too. Especially if other inconsiderate craft are nearby and moving with a large wake... Given that a 30 to 50 foot launch weighs in the order of 6 - 20 tonnes, that's quite a lot of force to be distributed back into the hull. The solution to this is to use a significant metal D shaped strip on the edge, and back it with hardwood, tapering down to thicker and thicker sections in softer and softer wood. This has the added benefit of increasing the walkable and usable surface of the edge of the boat from front to back. And the unfortunate side effect of increasing the beam, too. It also helps deflect water and protect the lower edges of the hull when rocking in close proximity.

On our boat it's built more or less as i describe above. It uses about 25mm brass D section, with countersunk wood screws every 200mm or so. This is good, but can bruise the wood if smashed hard enough, and could have been wider for more deck space and strength. The boat I found today did it differently. They have no wooden reinforcement instead relying on the structure of the hull and a 50mm wide polished stainless steel D with threaded rods or bolts securing it from behind. I like the 50mm nature of it, and the back bolting, and the look, however I dislike the lack of reinforcement and the price of stainless like that. Food for thought.

Author:  Fred [ Fri Oct 04, 2013 2:09 pm ]
Post subject:  Walk around

Walk around

In order to get from the front to the back quickly, and vice versa, you must navigate the deck on foot. Sometimes while carrying things, and other times in close proximity to a wharf with the boat rocking. As with the cockpit, it's important to have plenty of deck to stand on, not just for your feet, but also consider your shoulders and what you might carry. The belting helps space you out away from the wharf and give more foot room without compromising internal cabin space. However it's important that the cabin sides taper inward otherwise you may not be able to safely walk without holding on, which is sometimes necessary.

Author:  Fred [ Fri Oct 04, 2013 2:10 pm ]
Post subject:  Windage


For the boat to hang nicely from an anchor or mooring the bulk of the wind resistance must sit aft of half way. This means that you can not have your cabin extend too far forward, and you can not have your cabin not extend quite far back. From a style point of view, the cabin should take approximately one third of the length of the boat, with another third for the foredeck and the final third for the cockpit. My family boat has too much cabin, and too much of it too far forward, combined with a high front deck and long cockpit, she sometimes swings back and forward from left to right when anchored. This has an unpleasant effect on the occupants.

Author:  Fred [ Fri Oct 04, 2013 2:11 pm ]
Post subject:  Consumables


Water, fuel, LPG. LPG tanks must be in a sealed compartment with natural drainage to deck and eventually overboard. LPG is heavier than air, and if leaking, will fill up your hull and end badly for anyone nearby. This usually means they live near the cockpit in a cupboard of some sort. Water and fuel should be 1000+ litres each, and live in the centre of gravity of the boat so as not to affect the attitude of the vessel depending on how full they are. Putting them too far forward results in a bow down attitude and/or a very full bow which is ugly and inconvenient as various run-off angles are rendered useless. Putting them too far back results in large angle changes between low, and high. However there is freedom to move them around and be creative with storage (eg long thin tanks). Bulk weight like this is optimal in the opposite position from a car, for the same reason. IE, in a boat you want this weight as far from the centre as possible to maintain large inertia and reduce the magnitude of rocking movements for a given force.

Author:  Fred [ Fri Oct 04, 2013 2:11 pm ]
Post subject:  Driveline


Boats naturally have more floatation at the back. This makes the back an attractive place to put the heavy engine(s), however engines are often tall, and the back usually has little space from deck to hull. The back is also a great place to store things for quick access, whereas inside is terrible for that. Obviously the engine(s) can not reasonably go near the front of the boat. The further forward you put them, the bigger the problems you have with balance and a full bow unsuited for cutting into a head sea. And you can't really put them in the back, or your deck ends up too high, and you get no storage room back there. The only reasonable place is "near the middle" which poses its own issues. Shaft angle. For efficient operation, the propeller should be as close as possible to parallel with the hull which it is driving. If you could put the engine at the front, it would be pretty flat, but you can't. If you put the engines in the back, you use unreliable stern-legs, or you run a shaft forward to a V drive box, but we can't put them in the back. Forward of centre starts to affect balance, so the rear most position that doesn't affect storage is ideal. But if you do this, your shaft angle sucks. Thus I firmly believe that a V drive box mounted as far forward as possible, with the shallowest possible shaft angle, and the most rear mounted engine, is ideal. Gearboxes to suit this arrangement may not exist, though, however custom engineering could overcome that with enough desire.

Author:  Fred [ Fri Oct 04, 2013 2:11 pm ]
Post subject:  Refrigeration


There are three temperature ranges that you need to cater for:

  • Frozen (freezer -10to-20C)
  • 0C (Ice!)
  • Cold (fridge 2-5C)

Things like milk, meat, fish and some veges survive best at zero C on ice. Freezing things is not sustainable on a boat in any quantity and should be reserved for icecream and ice for GNT, only. Fridge temperature is also not sustainable, and is only really suited to some delicate veges, butter, currently in use drinks, etc. Ice is the preferred tool for chilling food and your catch, for longer periods, and is thus required in quantity. Our family boat holds about 3 cubic metres of ice, and my old man uses an EXTREMELY inconvenient and ugly plastic box to hold another 1 cubic metre. Hazards to ice longevity are weather conditions in summer, engine heat while moving, air leaks allowing melting, water build up promoting melting, and idiot crew leaving covers off for too long. Good insulation and isolation from the engine are essential, as are well sealed lids/hatches for access. The final aspect is the sump and drainage system. The pump must pull its water from a volume that can feed it without sucking air, and operate a float switch, and contain a strainer or filter. Insulation should exist on the bottom of the ice hold, so a portion can be omitted to allow an area for water to build up with a grill over it. Where this goes should be easy to access so it can be cleaned from outside the ice box as well as inside, should it block with fish scales, etc.

Author:  Fred [ Mon Oct 07, 2013 12:49 am ]
Post subject:  Sea Water And Air Flows

Sea Water And Air Flows

The engine needs air, and the exhaust needs to escape, and the engine needs sea water to stay cool, and that must come from somewhere, and you generally need a supply of sea water for cleaning things too, etc. You also need to get rid of sea water out of the cockpit and drain sinks, showers, and toilets, somehow. This post will elaborate on that, eventually, but for now, it'll just record a couple of points:

  • Exhaust should exit on the side, near the back corner, to avoid eddy currents bringing it into the boat.
  • Exhaust should have a significant rake down hill to the exit point to avoid back flow of water.
  • Water intake for cooling should be in rear 1/3 of the hull, and near the centre.
  • Water intake for cooling should be easy to clean marine build up out of.
  • Cooling water exits through the exhaust (of course)
  • Ditto for non-cooling like pressurised salt water feed for rinsing taps, toilet flush, deck hose, etc.
  • Air for the engine should come from a mid-high point on the vessel, top of sides, lower mid cabin, around there.
  • Air for the engine should follow a long path with mufflers to avoid deafening occupants.
  • Fittings on the bottom near the chine or too far fwd will back feed in heavy seas. Avoid this.

An idea I saw on a boat today was to use a chamber in the hull to suck water from, and to feed that from the bottom through grills. This isn't a bad idea at all, esp. if it can be sealed from the ocean for cleaning, and/or emptied and bypassed for lightening of the vessel/increasing flotation. On our boat we have a chamber like that but it's only used for live bait. To pick up speed/efficiency we sometimes empty it out and seal it up.

Page 1 of 2 All times are UTC [ DST ]
Powered by phpBB® Forum Software © phpBB Group