Quadrimaran: what do you think?

[double u]

..brilliant, DrHans! After dekades of moronic naval architects finally a genius.

[DrHans]

Originally Posted by ggray

Hate to be a naysayer, but as mentioned, you have an inordinate amount of wetted surface.

Length helps speed, resistance to pitch-poling, comfort, probably other things, more than does beam.

You are going to have more structural issues. Imagine being crossways in a wave trough, outer hulls pushing up and weight of inner hulls/cabins pushing down.

Many cats have berths in (on?) bridgedeck same as your model so wide hull or narrow berth is a not a relevant issue.

You are showing flat bottom hulls, not a good idea.

Big question is, for what reason do you need 4 hulls? Marina fees?

The wet surface may appear large, but is offset by an equally reduced draft; no cat of similar length and weight would only be 35 cm | 14” deep. The Qmaran almost hovers on top of the water.
Flat bottom hulls without rudders and propellers sticking out will ease beaching and reduce the risk of e.g. rudders hitting obstacles under water, or ropes getting stuck in your propeller. (Of course in reality the hull edges can be less sharp than depicted). Easy to add daggerboards in the outerhulls (e.g. dinghy garages) without any loss of functionality.
Since the span between hulls will be much smaller, strength of structural elements (with same height) will actually increase. The floorplan (with raised floors locally) allows for beams as high as 400 mm | 15”.
Obviously length helps speed more than beam, so you should compare against similar-length cats; therefore I compared against (for example) an Outremer 45 – being a top-end cat. See for example comparison-images below.
Marina fees will be low compared to the amount of extra comfort onboard. Moreover the large solar panels and double dinghies reduce the need for marinas in the first place.

[DrHans]

[DrHans]

[DrHans]

[valhalla360]

Originally Posted by DrHans

The wet surface may appear large, but is offset by an equally reduced draft; no cat of similar length and weight would only be 35 cm | 14” deep. The Qmaran almost hovers on top of the water.
Flat bottom hulls without rudders and propellers sticking out will ease beaching and reduce the risk of e.g. rudders hitting obstacles under water, or ropes getting stuck in your propeller. (Of course in reality the hull edges can be less sharp than depicted). Easy to add daggerboards in the outerhulls (e.g. dinghy garages) without any loss of functionality.
Since the span between hulls will be much smaller, strength of structural elements (with same height) will actually increase. The floorplan (with raised floors locally) allows for beams as high as 400 mm | 15”.
Obviously length helps speed more than beam, so you should compare against similar-length cats; therefore I compared against (for example) an Outremer 45 – being a top-end cat. See for example:
https://d2f0ora2gkri0g.cloudfront.ne...ba80457025.jpg
Marina fees will be low compared to the amount of extra comfort onboard. Moreover the large solar panels and double dinghies reduce the need for marinas in the first place.

While the individual spans may be shorter, if the outer hulls are on wave tops, you aren't reducing the stress on the beams by them being shorter.

It's generally not an issue beaching cats. Most people don't do it because they don't want to set down on a rock and punch a hole in the hull. This is solving a non-existent problem.

Flat bottom hull shapes are not efficient. Outside of barges where they are trying to maximize cargo capacity and planing jon boats, you pretty much never see flat bottom hulls. This isn't by accident. Once you correct this, you are going to be up around 2-3ft draft...very similar to a cat with boards.

Water jet engines are very inefficient also, so in solving a prop wrap issue, you are creating a new issue. Inefficiency happens every time you motor. Prop wrap while it happens is rare.

How will the rudders work if they aren't below the hulls?

I just saw the "dingy garage", are those leaving the dingy on it's side? How are you going to minimize chaffe? Looks like it would be a 1/2hr project to stow the dingy.

What is the overall height, where you are thinking of incorporating a 1.25ft beam? The picture looks really high sided.

With extra width, marina fees will go up if anything. At 28ft wide, side ties may be difficult to find in some areas as they need to leave room for the boats going by in the fairway. At best, it's likely a wash compared to similar size cats.

[DrHans]

[Redreuben]

No draft no skegs no boards, and no rocker. It will sail and tack like a raft.
Further, huge wave interference from the narrow hull spacing.
Best use is a houseboat.

[DrHans]

Originally Posted by valhalla360

A few thoughts:
- Flat bottom hulls aren't very efficient on sailboats. Change that and draft goes up.
- With nothing in the water, expect it to make a ton of leeway while sailing. You can add keels but then more draft.
- It won't have as much righting moment as a typical catamaran as much of the buoyancy is towards the center. I expect it to act more like a trimaran where heeling will be more pronounced.
- A shorter mast does not make for a lower center of gravity. In fact, it looks very tall which will make it a horror to dock as the wind can catch a lot of the high slab sides while there is little below the water to stop it.
- Beds on the bridge deck are pretty common. We had a full queen size on a 34ft cat. With a modification, it was possible to get your full 2m width.
- They can make cats wider but pitch poling starts becoming more of a risk than capsize.

This looks similar to some of the big trimaran designs. As the central hulls provide negligible righting moment, a single hull could take their place fairly easily.

Since you aren't trying to fit in any kind of slip, just go longer and leave the extra length on the ends empty (could go cat or tri for the same effect). It will add negligible cost or weight but significantly increase the hull speeds without nearly as much wetted surface issues.

Since the 4 hulls are narrow and sharp-edged each of the hulls – although flat-bottomed - may serve as a keel or daggerboard against leeway in and of themselves… Worth testing.
For performance under sail: easy to add daggerboards if needed in the outerhulls; plenty of space in the 2 dinghy-garages.
1 bed on the bridgedeck may be common, 2 also, but not Qmaran’s comfortable 4!
With equal sail area a shorter mast DOES make for a lower capsizing moment.
Just going longer would of course completely change the comparison, against much larger and more expensive yachts – needing a larger crew etc. And larger marina fees…

[DrHans]

Thanks by the way guys, for all your thoughts and comments so far!

[boatman61]

Great under power maybe, but under sail it'll suck..

[marcjsmith]

one of your unique attributes is that it is easy to build...


maybe I'm overthinking it, but getting 4 hulls built and aligned and joined together seems like anything but easy except for an experienced builder. and then finding a yard with space large enough to build it and launch, could also be a challenge..

[Kamen]

Why stop at 4? Is there anything special about that number?

[DrHans]

Originally Posted by valhalla360

While the individual spans may be shorter, if the outer hulls are on wave tops, you aren't reducing the stress on the beams by them being shorter.

It's generally not an issue beaching cats. Most people don't do it because they don't want to set down on a rock and punch a hole in the hull. This is solving a non-existent problem.

Flat bottom hull shapes are not efficient. Outside of barges where they are trying to maximize cargo capacity and planing jon boats, you pretty much never see flat bottom hulls. This isn't by accident. Once you correct this, you are going to be up around 2-3ft draft...very similar to a cat with boards.

Water jet engines are very inefficient also, so in solving a prop wrap issue, you are creating a new issue. Inefficiency happens every time you motor. Prop wrap while it happens is rare.

How will the rudders work if they aren't below the hulls?

I just saw the "dingy garage", are those leaving the dingy on it's side? How are you going to minimize chaffe? Looks like it would be a 1/2hr project to stow the dingy.

What is the overall height, where you are thinking of incorporating a 1.25ft beam? The picture looks really high sided.

With extra width, marina fees will go up if anything. At 28ft wide, side ties may be difficult to find in some areas as they need to leave room for the boats going by in the fairway. At best, it's likely a wash compared to similar size cats.

• Eventually a structural calculation and model tests will have to show what works best; long spans with fewer hulls or short spans with stronger beams. In general it is always more efficient to spread loads. ;-)
• (The height over the 1.25ft beams is located at seating areas front and aft, and a threshold under the rear mast)
• Each set of hulls on one side can be seen as one floater – and suddenly the Qmaran looks much more similar as cats again, with similar forces.
• Water jet engines are very common in power boats already, so they could very well serve sailboats too. Especially since the Qmaran is half a speedboat already ;-) Many ferries are jet-powered multihulls nowadays.
• Prop wrap may not happen often, but when it happens it is often very inconvenient and risky – certainly worth avoiding.
• Since the rudders don’t stick deep, there are more of them to compensate. You don’t need much surface to steer properly.
• Chafing a dinghy is not any more issue whether a dinghy garage is horizontal or vertical. It is just different, that’s all. No cat or monohull of ~46 feet has two dinghy garages measuring 3x2x0.6m anyway.
• When mooring most quais (e.g. in the Med) a few feet extra will not matter much. But it will give plenty more comfort aboard.

[DrHans]

Here you can imagine where the higher floorbeams fit in the elevated floors: