Pocket cruisers

[Raggi_Thor]

I think a cruising speed around 20 knots is more than enough.
Then you burn half as much fuel per mile as you do at 28 or 30 knots.
You can have 25 or 30 HP per ton instead of 60.

[Willallison]

As always Tom's bang on the money with all his comments. My Searay, for instance had a minimum sensible planing speed of around 17 knots. I could keep it on the plane at slower speeds than this by trimming in the leg and applying plenty of angle to the trim tabs - I could get it down to around 12 or 13 knots in fact. But the fuel consumption would have been horrendous.
It's really a matter of determining what kind of boating you want to do. I bought the Searay in Sydney, where we operated it for a couple of years before bringing it home to Tasmania, where we used it for a further couple. We often spent up to a fortnight on board, but almost all of the cruising was in sheltered waterways where the biggest seas we were likely to encounter were the wakes from passing boats. It was an ideal boat for for that. I cruised at 20 - 24 knots.
However, it was definitely not a boat for doing extended open-water passages, where it might be necessary to slow to low planing speeds.
For this (if you set aside true displacement boats) then you really want a boat that will be both efficient and comfortable at anything from 10 to 20 knots. To achieve this isn't rocket science, but it does require a commitment to the "Less is More" principle.
Primarily, the boat MUST be kept light.
It should have a relativley high length/beam ratio
And, unless you prepared to accept high levels of trim, it must have low transom deadrise.

[Guillermo]

Well,
Here you have the lines for the before mentioned WHIO, designed by Bill Simpson & Peter Sewell. Big L/B, slender hull, planning surfaces aft, canoe stern and very light cold molded construction.
In the pursuit of lighteness, she even doesn't have a steering wheel, but a wooden staff mounted to starboard of the steering position. She does 17 kn with just 50 HP and uses half a US gallon/hour at her cruising speed of 10 kn.
Peter also designed and built the propeller, claiming an 80% efficiency.
The boat can go astern at 12 kn!
I find this boat quite a nice piece of design and engineering.

[quote=Guillermo]Having opened a thread at the Sailboats forum about small seaworthy cruisers, I've considered the oportunity of also studying this concept for the motoring side of it.

So I propose now a discussion about 'pocket motor cruisers' understanding the term as motor boats under 30' able to do extended coastal crusing for a family (Up to 4 people), so not runabouts or dayboats, in a safe and efficient way......

What about this design:

Van De Stadt: http://www.stadtdesign.com/products/vds608_6531.htm
in drawings the 9,50 concept
in picture on sea trial the built wood core 12 mt
in picture on yard the smaller 8,50 begin build by AB (picture of plug/mould)

[Guillermo]

Thanks Luigi. Very interesting boat with a different and intelligent lay-out. From Van de Stadt's pages:

Design 653
Length over all 9.50 m
Length waterline 9.35 m
Beam 2.40 m
Draft 0.55 m
Displacement 2.00 t

A pity they do not state more info, as power, speed, range, etc.

Design 608 (out of the range of this thread)
Length over all 12.00 m
Length waterline 11.80 m
Beam 3.00 m
Draft 0.70 m
Displacement 4.00 t

Keep on waiting for your Lobster Boat's info.
Cheers.

I will come back with full specs, we are setting up frame for the 9,50. Moulds of the 8,50 (but it is just a small launch) is already finish

Anyway basic parameters of these projects are:

- light construction with modern composites
-classic design
-sailing boat type hull with round bilge easy planning at low speed (very low power planning hull)
-fuel efficiency
-trailerable, even the 12 mt, as very light
-simple but nice and classic interiors build with modern composites (visible on http://www.yachtdimension.nl/, cobuilder promoter)
-capacity of coastal and offshore passages (the 12 meter make Holland - UK trips, 35 + knots with single 250 hp)

some updates :
sorry for the mistake, top speed of 40 ft is 33 knots with 250 hp
max speed 33 knts

fuel consuption at cruising speed 25 knt 25 liters, at top speed 40 liters

total weight 3300 kg
I will come back with more specs for the 9,50 meters project.

[yacht371]

Check out the MC29 Power catamaran at www.aviadesign.com. It has about the same fuel consumption as WHIO, a higher top speed and meets the 4 person accommodation requirement. It is a GRP production boat so available to many who might not want to build their own, or can't afford a custom boat.

[Guillermo]

Thank's a lot yacht371
(Sorry, I'd love to have used your real name, but the nick is all I have)
Very interesting design. I think it would be great if you broad here design and test details related with load and speed, as those are not clear in your web pages. I'd also like to know load carrying ability, if possible.

LOA 8.88 M 29'-1”
Beam 2.60 M 8'-6”
Draft 0.47 M 1'-7”
Disp. 1800 kg. 3960 lb. (I asume this is in lightship condition )

From Avia Design's pages:
"...Planing hulls are usually very poor at this, frequently requiring 20 mph or more for good running, and "mushing" badly at lower speeds, with the bow high and attendant poor visibility. Yet I notice that most cruising power boats seem to run between 10 and 18 mph, the least efficient speed range for a planing or semi-displacement boat. The narrow displacement hulls of a Motorcat are at their most effective in this speed range."

"...actual figures for the Volvo D3-160 diesel version...efficiency in the 10 to 20 mph range is outstanding."
RPM MPH L/h Gal/h MPG
1000 6.9 1.2 0.32 21.6
1200 9.2 2.5 0.64 14.4
1600 11.5 3.8 0.98 11.7
1900 13.8 6.3 1.63 8.5
2150 16.1 7.0 1.81 8.9
2500 18.4 10.0 2.58 7.1
2750 20.7 12.0 3.10 6.7
3000 23.0 15.0 3.87 5.9
3400 25.3 23.0 5.94 4.3
3800 27.6 27.0 6.97 4.0

More at:http://www.aviadesign.com/MC29Perf.htm

[yacht371]

The MC29 was tested at about 2000 Kg. weight(based on where she floated) with 4 persons on board. In about mid July we will have one(single diesel version) in Vancouver BC where more extensive sea trials will be conducted. We haven't tested her in large seas yet.

Once there are more details they will be posted on the Aviadesign web site. You probably already figured out who I am.

Grahame Shannon

[Guillermo]

Originally Posted by yacht371

...In about mid July we will have one(single diesel version) in Vancouver BC where more extensive sea trials will be conducted.....

Thanks, Grahame. WE'll keep on waiting for those tests' results.
Cheers.

[Zewe]

I'd be interested in feedback regarding Sea Bright Skiffs in the context of this thread. I understand that this type of hull is quite efficient in the speed range that is being discussed, and can be more seaworthy than other designs that are offer similar efficiencies. One example:

http://www.boat-links.com/Atkinco/Cruisers/Naiad.html

Comments?

Randy Foster

[Willallison]

I have no experience with the sea-bright skiff, so I can't help you there - sorry
But something caught my eye in the drawings on the link to the Naiad that you posted, is that the shaft appears to be set at an angle.
This is something that I've never come across. I assume its been done to try to offset the torque of the propeller, but I'd be concerned, particularly at speed that it might have some rather dire consequences

[Gilbert]

What sort of dire consequences are you expecting?

[Guillermo]

Originally Posted by Willallison

I have no experience with the sea-bright skiff, so I can't help you there - sorry
But something caught my eye in the drawings on the link to the Naiad that you posted, is that the shaft appears to be set at an angle.
This is something that I've never come across. I assume its been done to try to offset the torque of the propeller, but I'd be concerned, particularly at speed that it might have some rather dire consequences

Yes, I find that quite strange, too. Propeller doesn't seem to be that big and power is not so high.... Coming from a reputed designer as William Atkin, I would like very much to know the reasons.