More Option One

As far as the two speed thing is concerned, it might just be possible with a 10 or 20 knot cruise - not with a 35 knotter. As Tom has said previously, a deep V is the only obvious monohull option for that - and they don't tend to be too good at 10 to 15 knots - at 6 maybe but not much faster. Which brings us to the catamaran option and here lies the great advantage of the cat - you can power a given catamaran to achieve virtually any speed you desire without huge penalty, particularly the displacement type hulls like those developed by Malcom Tennant.

Tom, I'm a little confused here. At rest a deepV with its chines clear of the water is a bugger of a thing - rocking and rolling at the slightest movement. At this point it does indeed need to be heavy enough so that the chines are immersed. But as it goes faster, the dynamic forces acting on the hull will make it rise upwards. The faster it goes, the higher it rises until it gets to the point where the forces pushing it up cease to exceed the forces of weight which are pushing it down. There are many good handling Deep V's which run quickly with their chines well clear of the water - they may well have running strakes to aid with both lift and lateral stability, but their chines are out of the water. I used to do a bit of ski racing. The boat I skied behind was a 20foot DeepV. Running at about 65mph there was onlya few inches of the bottom in contact with the water, but the boat was as steady as a rock.
I don't doubt your knowledge on the subject, so I must be missing something - can you expalin a little further?
I had trouble finding a good pic of a boat going quickly to demonstarte my point - everybody loves to show off their boat either bashing thru a wave or flying off the top of one! This pic shows a Deep V running in calm water - there is plenty of spray coming into contact with the chines, but they are well clear of the surface

 

Can it be done he asks? If you built the hull of glass over foam, it would be two things low cost and low weight. I’m sure we could find a proper layup that would hold together at these speeds. The skill level would be moderate, but the man hours would be high. So a home builder could do it with our budget, allowing 25K for the drive. That is of course not allowing for Paul’s communication system. The interior would be a little spartan, but you could add things as you go.

The rendering you have posted Will, looks to be developable. If it is, the construction should not be too hard. Can 300hp push that baby to 45 knots?

I would think the narrow beam would rule out a cat.

I ask my self what I am doing here. I’m just a builder of canoes and row boats. Way out of my league this time. I’ll be back on Monday with more questions I’m sure.

Gary

 

Gary,
You are right - the entire boat is made up of developable surfaces. As far as construction goes, I had the same sort of thing in mind as you. Bearing in mind the I haven't done a proper weight estimate, the displacement I have based my calculations on is 2000kg. That would require 165hp to do 35k, 275 to do 45k.

 

Will,

We can all learn new things and I am certainly no exception. I don't doubt your deep V running with only a few inches of bottom in the water but that has not been my experience, so I will defer to your judgement on that case.

In watching many racing deep V's at speed, several things come to mind. The hulls do have lots of horizontal surfaces in the form of lifting strakes. The boats are designed and built with the weights centered and low in the hull to gain stability. They are driven by a one throttle man and another who only steers. They are anything but stable at speed and dance all around under the influence of assymetrical wave action even with the 100% attention of two pilots. In addition to the above, the system greatly compromises efficiency for speed in rough water and pays a stiff price in reliability, power, cost and fuel.

In a cruising boat, only a little attention will be paid to weight placement after it has been built. When underway, people will want to move about and not upset the balance. No one wants to be steering a boat for hours on end that requires the kind of attention that a race boat needs.

I have nothing against deep V's in the areas where they excell. That is, waves and high speed. In protected water and at moderate speed I think they charge too high a price for a cruising boat. I would consider using a deep V for a cruising boat in the water that I am likely to choose to be in a bit like driving a Surburban or Expedition to the market down the block for a carton of milk. And yes, I also see that every day.

Gotta go out of state for mother's day. She was 94 last week and still expects me to drag my old bones down for a visit. Carry on without my sniping from the sidelines for a spell.

 

Cat versus Monohull

Another problem with trailerable catamarans is the hulls and the trailer wheels tend to compete for the same area. For maximum stability they both want to be as far outboard as possible. A monohull can nest nicely between the wheels, which allows it to sit lower on the trailer. This helps at the launch ramp, improves stability on the trailer and bridge clearance.

I have found that the key parameter for wet launching is the waterline height off the ground when the boat is on the trailer. This tends to drive the required water depth for launch. Of course this is more of an issue on deep draft vessels than on shallow draft boats.

Cheers;
Mike Schooley

 

Tom, Will, Gary some very impressive points and I side with just about all of them. Mike yours is a good point but this just like your Trawler would not be toted around like a dingy. It would just be avabile if it was desired.

 

I don't disagree with your point, but I think the issue is still relevant. Although it depends on the planned usage and distances you plan to haul the boat.

My Trawler will live on it's trailer. I figure the savings in slip fees and bottom paint will cover more than half the truck payment. In addition the boat will get more attention parked next to my house than in a marina 45 miles away.

I plan to launch and use it one weekend a month locally and 3 to 4 weeks of vacation per year. The vacation trips will generally be thousands of miles from home and sine I live on the West coast I'll need to traverse mountain passes with steep grades and strong winds. In my case trailer-ability is quite important.

I'll be traveling for the next two weeks (unfortunately not by boat, so my participation will be limited. I'll support what ever the committee decides.

Cheers;
Mike Schooley