Pocket cruisers

Maybe not. See attached photo. As a matter of fact a client of mine mounted the thing in a 6.4 m boat and he trailers it without problems. I think it's a matter of having the adequate trailer.

I do not like having petrol on board, so outboards are out of the question here. The 'standard' inboard engine and straight shaft installation is a cheap and sturdy solution (KISS principle), but clearly space is a concern here.

JetPac will not allow for hot water generation, but this is not important to me, as water consumption should be kept to a minimum, because of weight reasons (Showers: Ashore).

Sterndrives are cheap, but less efficient and prone to problems. I do not see a sail drive here either.

I'll keep on working on the thing. Maybe it's time for some drawings....

 

For the jetpac, I am still dubious. I speak of a boat about 9m or 9.5m length, weigthing 2 tons on the trailer. But 400 kg are overhang at the rear. And that leave only 1.6 ton for the boat. If that means a special custom made trailer, it reduces the interest of trailerable boats.

I also see clear advantages for the jetpac on boats where it is very complex to put an inboard, such as RIB or inflatables, or when you already have an outboard powered boat, and you want to change.
But when at the design stage, why would I prefer a jetpac over a classical inboard with a jet propulsion , when the boat can allow a classical stern inboard ?


Back to the layout with a straigth shaft. The logan 33 solved the layout problem by using an extremely long shaft allowing to put the engine under the fore V berth. What I do not understand clearly is how they solved the headroom problem. Seems that the cabin floor is at the same level in the firt or second cabin. There is the prop shaft under that floor. In the pilothouse, the headroom is correct, but in the front cabin, it should be short. But they probaly have headroom in the head. So I guess that the floor of the head is lower than the floor of the passageway, and the hull is deep enough to have headroom with the lower roof. So they may have a Cp in the 0.5 0.55 range, more of a sailboat than a semi displacement boat. (fine entries, deep hull). This would be consistent with the slow speed they have. It is a pure displacement / very low power hull, not a semi planning one.

And for planning hulls, there are photos of Dorado 30, planning hull, 9m length, 2.5m beam and 2.5 t. But the cruise speed may be higher than the 18 kts Guillermo is seeking for. And the accomodation a bit less. The headroom would be difficult to solve.

 

QUOTE=fcfc]
Back to the layout with a straigth shaft. The logan 33 solved the layout problem by using an extremely long shaft allowing to put the engine under the fore V berth. What I do not understand clearly is how they solved the headroom problem.[/QUOTE]

This is the way to go, and it doesn't seem difficult to solve the problem.

If you look at the Andreyale 10, you are going to see that they have gone in the same direction.

This is just theoretical or you are thinking in making a boat along these lines?

 

Barely. The andreyale 10 does not have headroom in the head. And going from saloon to head means going outside. They have a bigger engine (60 -75 hp) than the lombardini 40 hp from the logan 33, and they did not put it under a berth, although they put it forward. They need their front cockpit.

Theorical and learning. I may play with FREE!ship, draw some lines, and eventually in the best case, end up with a R/C scale model. But no further. It is not my job.

I am not Naval Architect, but I know enougth to know there are in boat design some gory details I do not want to / cannot dig inside. Say weight and balance, building schedule/sequence for minimum time/machinery or corrosion/rot problems.

That s not for me.

 

Yes, but at least you have good sense

Seriously, the boat you want can be made. With headroom in the forward cabin, it will be probably ugly (at least for my taste), but perhaps you can have a big forward cabin without headroom (1.6M or so), and the rest is easy. You just have to have a long forward cabin, and a storage space at the bow to permit the engine to stay under the bed and even so, not to much in the front of the boat.

Of course, the interior and exterior design of such a boat is not difficult, but the calculations for the weight and balance of the boat are another story. You need for that not only a naval architect but one that have experience with this type of problems in this kind of very particular boat.

Joubert-Nivelt would be perfect....so, you can manage it if you pay the work.... and it would not be necessarily a complete project, but only hull and weight distribution, over some drawings provided by you. About building the boat there are plenty of small shipyards that have enough knowledge to give you a quote and sufficiently experienced to take care of all the details, even if the plan is only complete about the hull and weight distribution.

The only catch is that it will cost you a lot more than what you want to spend

 

Speed and efficiency vs Hull shape

For every speed/length ratio there is an optimum prismatic, LCB and volume distribution (curve of areas). Thus the optimum cruising speed should be chosen before anything else. Narrow displacement hulls can be more efficient than planing hulls up to a s/l ratio of around 3 (16 knots on a 28' WL). This is because the planing hull is not really "up on top" until beyond that speed.

Discounting catamarans, there are several ways to make narrow displacement hulls that have adequate stability. One is a power trimaran, with a narrow efficient main hull and a pair of "training hulls" which just kiss the surface. They need not be nearly as wide apart as a sailing tri, just about the same overall beam as an average monohull (3:1) should work fine. Unlike the catamaran this lends itself to very low CG since the narrow, fairly deep main hull will allow engine and tanks to be low down. I would stick to a semi-circular section to keep wetted surface to a minimum but use a higher prismatic and less rocker than a sailing hull.

A "planing" hull which does not have a "hump" in the speed curve and runs very well at s/l ratios from 2 to 5 is the patented "FlowMocean" design, there is an example on my web site www.aviadesign.com, the originator is Peter van Diepen at www.naviform.com

Another hull form which allows good performance in the speed range just above full displacement speed is the "displacement glider" (google the term). This is an Austrian design. Utilizing the same principle but a different shape is my own "powerkeel hull".

Propulsion: You can't beat a diesel with duo-prop for pure weight/fuel use/thrust.

Jet drives: I have owned a jet boat with a planing hull. Although great fun when viewed as an amusement park toy, the jet drive exaggerated the worst characteristics of the planing hull. At 1000 rpm the boat did 5 knots, at 2000 7 knots, at 2500 RPM, 8 knots, then bang a slight increase in throttle to 3000 RPM and you were doing nearly 30 knots. It was impossible to go 15-20 which would have been a nice cruising speed. This is because the jet is very inefficient until it reaches a fairly high critical RPM, then watch out. The planing hull also behaves like that, bad combination unless you want to go 40 knots all the time...

Outboards: modern 4 stroke outboards are quiet smooth and fairly fuel efficient. I like the Yamaha Hi-thrust 60, we tried two of these on our MC 29 "test mule" and got 16 knots on just one engine, we don't know the top speed with 2 as the engines hit the rev limiters before we got there. We will have to try again with more pitch. Still, fuel consumption will be 50% more than a single diesel, weight about the same.

For a true planing hull the one I have had the most success with (smooth ride, good handling and fuel efficiency) has a 24 degree deadrise at the transom, wide, deep chines so they stay in the water, and a center flat from midships aft (delta pad) which adds a lot of lift. This 25 foot boat runs great, is stable at rest, and does 33 knots with 230 HP (2 X 115 Yamahas). Video at http://www.c-kingmarine.com/video/cking-mr-video.htm

One trick used on this boat, and others I have done, is to angle the spray chines upward 5 to 10 degrees at the bow and then gradually flatten them out aft. This throws spray aft rather than sideways, and also stops the chines from making slapping sounds at anchor.

Sorry to be so long winded--they used to call me "the professor") when I was 6.

-Grahame Shannon

 

Nice post, Grahame.
Interesting the FlowMocean hull, but I think I've seen this kind of hull before. I have to find out where....
Nice boat, the Marauder 250, Do you have a layout we can have a look at?

About your jets commentary, I've personally tried the JetPac 150 diesel in two different boats, and speed increase up to 28-30 knots was quite smooth passing through all the intermediate range. This equipment is quite effctive at slow speeds due to its relatively big impeller diameter (250 mm). What kind of jet drive did you own?


fcfc,
I love the Logan 33, but I'm trying to tighten here to boats less than 30' and these last posts specifically to no very fast planning boats.
On your question... "why would I prefer a jetpac over a classical inboard with a jet propulsion?", simplicity is the answer, as well as lower price and free space aboard. Which is not little....

 

Well, you can continue to teach. It is a very interesting post.

!6 knots on a 28 ft boat and low consumption would be great.

Can you look at the drawing at post 91 on this thread and comment on the engine localization? I know that the boat works fine and makes 15k with a 60hp engine (it is designed by one of the best French Architects).

That boat has the engine in a very forward position. Do you think it is possible to put that engine even more forward? What are the implications of having the engine in that place?

I have googled for "displacement glider” as you said and its all very impressive:

“As the diagram illustrates, DG achieves in the transition speed range significantly higher speeds than both the displacement and planing boat given the same power input.

The DG-effect is valid throughout a wide speed range: for a boat of 14.6 m it is 9 to 19 knots.

The DG prototype achieves a maximum advantage over other hulls of approximately 30 per cent of power at 16 knots.”

http://www.alsphere.at/dg/performance.shtml

I don’t see why a DG (displacement glider) would not perform well in a 28ft, what do you think guys?

(Thanks for the suggestion Shannon, it seems very interesting. I have seen that you have done some tank testing with a dg model with impressive results, it would work with a 28ft?, or do you think the "FlowMocean" is better for this size? Can you compare both systems on a 28ft?)

some pictures of a DG hull:

 

Flowmocean vs displacement glider

The Displacement Glider and Flowmocean hulls are both suitable for smaller boats below 30'. Based on my tanks test I would say the displacement glider type of hull is better in the below 15 knot range than the FlowMocean. However at about that speed the FlowMocean crosses over and is better up to about 30 knots beyond which a deep vee takes less power. Both FlowMocean and Displacement Glider boats are quite superior to full planing boats in the below 20 knot range.

Here is a picture of a Flowmocean hull with an inboard diesel jet drive, 23 feet long.


This boat suffers from the jet drive problem I alluded to in my earlier post, in that it doesn't want to go slow. I would prefer a stern drive. Another problem with jets is they lose steerage when you cut the throttle suddenly, the natural reaction when faced with an obstruction. I never hit anything because of this but I scared myself a few times! They will crash stop fast though, just throw it in reverse.

My own jetboat was this one:

That isn't me driving, I have more hair! This was powered by a 175 HP Mercury jet drive, a lot of power for an 1100 lb. boat, top speed 50+ knots. But nothing happens til 3000 RPM then HANG ON! I decided I'm too old for this type of boat. It was a 6.5" impellor. There is no doubt a larger and slower turning impellor would be better in the lower speed ranges, but I can't imagine it ever having the kind of "grip" you get with the Volvo Duo-Prop stern drive.

Marauder 250 layout, a typical West Coast boat...

This was the preliminary layout but the final is essentially the same. 30' with a 10' beam would allow a nice cruisng layout in this hull.

Grahame Shannon

 

Flowmocean and Glider vs Seabrite

Hi Grahame,

Do you have any experience with the Atkin seabrite style of hull form? Any comments that might compare them to the Flowmocean or Glider concepts?

Thanks

 

I don't have any experience with that hull form, but it seems to be the Grand Daddy of the displacement glider hull form, so it could be expected to have some of the same characteristics.

Many older powerboat designs are quite efficient as they didn't have today's light and powerful engines to work with. One yacht designer I sometimes do hulls for laughs at my efforts to produce efficent hull designs. He says many naval architects are idealistic about this but the clients don't care, they just order bigger engines if they want more speed.

Weight is the big enemy of speed. Unfortunately bigger engines weigh more and use more fuel so bigger tanks (always kept full) are in order. One of the fears we have with the MC29, which due to very carefull management of weights, is very light, is that owners will fill up all the available storage space, which is considerable, with heavy stuff, and then complain that she doesn't go! It was designed for 2 x 50 HP inboards or a single diesel but we have already had people ask if we can put 150 HP outboards on. The answer is NO!

 

This 28 ft hull should reach 16 kts with about 45 - 50 hp.
http://www.admiralstender.nl/defaul...l=page:core:page:12:Webpagina:&sitelang=dutch
It is lighter than a Andreyale 10.

BTW, I am not sure Andreyale are not planning boats optimized for slow speed. The image below is Andreyale 15. You will see here Andreyale 12 with twin 175 hp for 24 kts and cruise 18 kts. http://www.castlemain.net/brokerage_caterina.htm
Definitely above rangeboat 12m which is optimized for 13 -15 kts with smaller engines.

 

Consider the alternatives...

As Tom stated in his recent post – this thread has been all over the place since I checked in last.

The following is just my personal opinion – FWIW – YMMV and all other applicable disclaimers.

Each person contemplating buying or building a boat has a different idea of what constitutes a suitable boat for their personal use. This is true no matter whether it’s a one-off design ala Whio, or a mass production boat that they espy at the local boat merchant.

The designs available at the local boat merchant reflect (at least here in the states) the (seemingly) inherent human nature desire that equates bigger, faster and with more “stuff” as being superior to other alternatives.

Tom Lathrop and his Bluejacket designs are the antithesis of this sort of logic. Tom’s design appears to meet some specific design goals extremely well. But it is what it is – and Tom has shunned trying to design a boat to be something for all people. If you can embrace Tom’s design criteria, (http://www.bluejacketboats.com/designing_liz.htm) then (IMO) Bluejacket is a “perfect” pocket cruiser boat. But if your wants/desires/needs are different, then… we move on to something else.

That brings me to four essential (in my mind) questions one must ask before buying or designing/building a boat.

1) Where do you want to go?
2) How fast do you want to get there?
3) How much “stuff” do you want/need to tote along?
3a)What is your amenity comfort level?
4) How independent of support services do you want to be?

One question at a time.

1) Where do you want to go?

If I want to go Tuna fishing 150 miles off the coast, that desire requires a far different design than if I want to cruise coastal bays and estuaries and the ICW.

Personally, I’m infatuated with Alaska and The Inside Passage. Lots of different boat designs/types/sizes make that cruise every year. The last boat I was on in those waters I had to dress for dinner and the cabin was 3 times as spacious as any trailerable boat will ever be!

But I want – almost have a primal need – to go back and explore the NW coast of British Columbia and SE coast of Alaska. Not once, but numerous times. And a 800’ cruise ship is not the way I want to go – there is no way to get up-close and personal with the islands, bays, fjords and waterfalls on one of those behemoths, regardless of how good the food and service is.

These folks - (http://www.geocities.com/bill_fiero/index.htm) and (http://www.georgeberotti.com/2Wander/) are doing it in 22’ boats. Please do “invest” the time to thoroughly peruse their sites, as their adventures and the documentation thereof are worthy of much wider recognition and praise.

So BC/TIP/Alaska is doable in a 22’er. 2) How fast then?

In this case, the C-Dory is reasonably capable of 15 knots – give or take. And that’s OK by me. But I also think that slower (reasonable) displacement speeds for a 28’er – 6 knots or so might be OK if the answer to question 3 and 3a is “lots”.

3) In the links mentioned above, it seems that these folks are pretty minimalist in their required “stuff” and comfort needs. Is the choice of a small-ish planing boat and the need for lightness right for me? Not enough data is currently available for me to make that decision right now. But I do recognize that it is a vital question that has wide-ranging repercussions across the entire range of design choices.

4) Finally, me thinks that if I’m so attracted to BC/TIP/Alaska that I must be prepared for most any eventuality short of replacing a motor in a remote fjord. That feeds back into question 3) – how much repair/distress “stuff” do I need to tote? As with all things boaty – one choice drives other choices and on and on.

So where does this leave us in this Pocket Cruiser discussion? Given the questions above, and the immutable fact that one design can’t be suitable for all conditions, it seems to me that instead of going all over the place with ideas, it would be much more productive to clearly state the design criteria and go from there.

Initially, Guillermo stated; “So I propose now a discussion about 'pocket motor cruisers' understanding the term as motor boats under 30' able to do extended coastal cruising for a family (Up to 4 people), so not runabouts or dayboats, in a safe and efficient way.” And further, “Boats for coastal cruising in general.”

Then Tom Lathrop and Williamson said, in effect, “Narrow the design parameters so we can have a reasonable discussion.” And then the thread went to wrack and ruin from there. {edit - for those that are irony challenged}

While certainly a wide-ranging and interesting discussion, I wonder if it’s useful in any way other than people posting pictures and providing links to (in their opinion) suitable candidate boats and designs?

So do we continue here? Revisit option one? Start a new thread with tight usage/design criteria?

I don’t know. I have no answer so I’m just going to drop this little doggie poop message here and run away from computers, the Internet and discussion forums for a couple weeks of badly needed R&R.

Best to all,

Leo

 

The thread has not, in my opinion, gone to wrack and ruin. Quite the contrary we have discovered the range of what constitutes a "pocket" cruiser. It is evident that some have bigger pockets than others. I used to consider a 30' boat quite a substantial yacht!

Anyway, I would like to introduce what may be the finest example I have seen of a pocket cruiser. It is written up in the June 2006 issue of WoodenBoat. WHIO is nearly 30' long and burns only 1/2 gal. and hour at 10 knots!!! She does 17 knots with only 50 HP. And she is very good looking to boot. http://www.steamlaunch.co.nz/Whio.html

How is this remarkable efficiency achieved? Light weight is the first thing. She weighs only about 1/3 as much as some other boats this size. The hull is a very fine example of a semi-planing or semi-displacement shape.

Disadvantage: you have to leave most of your "stuff" at home. My own feeling is the more stuff you have, the less value any of it has. Having just one source of propulsion will encourage good maintenance. A small capacity for foodstuffs encourages us to lose a little weight. No shower? Go for a swim.

It seems to me the under 30' "Pocket Cruiser" could be either a tubby "mini-trawler" capable of carrying lots of gear and fuel at 7 knots, or a faster lighter boat like WHIO or the MC29 which gets you there quicker, so you can spend more time relaxing, swimming and hiking.

My vote goes for the latter. If I'm going to go 7 knots anyway, I would rather sail.

 

Irony:

1. The use of words to express something different from and often opposite to their literal meaning.
2. An expression or utterance marked by a deliberate contrast between apparent and intended meaning.
3. A literary style employing such contrasts for humorous or rhetorical effect. See Synonyms at wit.