Playing around with a 10 m trailer cruiser

The steel towing bracket and the vinyl pool liner are not the best of friends. Tennis ball serves to keep the disagreement from turning violent.

Thanks
As for yellow.... good question. Maybe to make it easier to find when it breaks loose? More likely (and the actual reason in my case) is to provide good contrast with the wake for photo/video shooting.

 

Nice looking boat. I read your post and all the replies. The hull shape looks very slippry and easy to propel thru the water I would think that it would not burn too much fuel. I look forward to reading about your test results.
I would like something similar for my next boat. Similar size, 34' LOA 9.5' beam, but optimized for 8 to 10 knots. About 10000 lbs displacement. Just a dream on my part. But your work is an inspiration to me
Thanks,
Chuck

 

Thanks for the kind words, Chuck. I'll keep everyone posted on how things come with this one. If you want to see inspiring work, though, go ask Tom Lathrop (he actually followed through on something that started as a concept like this, and has been cruising on the result for a few years). Or Phil Bolger, or that Willallison guy who's been hanging around this thread . There's some seriously dedicated designers for you....

 

I'm retired and on a very limited income. I also live aboard full time and that adds some complications. Although I live very simply, you still have to have a full galley and head, decent sleeping accomodations and a place to lounge around down below. My biggest stopping point is that I would have to build out of wood (no problem skill wise) and the finished product no matter how beautifully it was built and how famous the designer is would not be worth even the cost of the materials and may only be saleable at a fraction of the cost of materials. But I still may do it. Atkin's Dancing Feather design looks to be close with a different cabin layout. It's designed for the speed range that I want. There other designs out there that would also probably work well.
I looked at tom Lathrop's blue jacket boats and they are too small. I also don't want to go that fast. Beautiful boats though. 8 to 10 knots is just fine and in my primary cruising grounds of the Sea of Cortez, you can't even go that fast when a norther is blowing and you are bashing into the 3' to 6' square chop that passes as waves. Imagine the wind chop on a lake and then increase the size to 6'.
I like what Tad has to say and some of his designs, but a custom design is out of my budget.
Well keep up the good work and I look forward to your furture posts.
Chuck

 

Tests!

Well, we had the towing rig and model out on the lake today for some preliminary testing. And it works!

Around the dock, the 3-point harness is a bit of a handful to control. Once there's a bit of drag on the model it works beautifully. We ended up cleating off the bow line and hand-holding the side lines; this enabled the person up front to not only steer the model but also to try inducing directional instability. Took a bit to get used to, but it is working quite well. The towing rig, of course, needs to be modified to be a bit easier to handle dockside, as a truss of 2x6 lumber sticking out 8 feet to port not only induces a bit of a list in the tow boat, but is a bear to mount and dismount. It's designed to be foldable so I have to get that working now.

Today's runs were mainly a 'proof of concept' and we didn't have accurate logging equipment on board; speeds indicated are very approximate as a result.

We started with 4.6 kg of ballast right in the stern, putting the model a hair above scale loaded weight and trimmed almost exactly level at rest. The model tracked true from idle right on up; we could pull it off track with the side tows but even though we kept the bow tow slack the whole time, it held a nice straight line. We had 5-10 cm waves at first (approx. 30-60 cm scale); it handled this nicely. The model doesn't have a spray rail; it is quite obvious that the real boat will need one, but most of the spray did go to the sides and very little came over the deck. The side towing brackets, of course, churn up a fair bit of spray. We got up to approx. 9 knots (scale speed of 20 kt) with this; bow-up trim was getting excessive though.

Moving the ballast to get the centre of gravity at around 36% of LOA (38.5% of LWL) brought the maximum bow-up trim to around 3 degrees (another to-do, add a trim indicator). We came close to 10 knots (scale speed 22 kts) like this with no directional stability issues and no porpoising. I'll have to borrow a GPS from somewhere to get better speed numbers of course; my pitot-type speed log isn't very accurate below 10 knots. We had a very hard time discerning a planing 'hump' in this condition; the bow wave of the model is so small that it's hard to tell exactly when it is crossed. (We were up to an average wave height of approx. 10 cm by this time, or "2-foot chop" to the real boat, with the rougher patches and boat wakes being equivalent to 3- or 4-foot seas.)

So apart from some glitches with the dockside manners of the rig, the model performed very well in preliminary testing. Next steps are to get some good speed and trim measurements, and different sea states (calmer seas would be especially useful).

I tried to upload a couple of short video clips of the testing but it seems *.mov is an illegal format here? Anyway, the attached pic is with CG at 36% LOA and somewhere around 16 kt scale speed.


On a slightly different note, simulations on the 8.5 m version (which is currently looking like the most probable to be built) are suggesting it will need 37 kW at 20 knots and 57 kW at 25 knots in nominal loaded state (2370 kg). Figuring on a total propulsive coefficient of 0.5 for jet or prop losses, skeg/gearcase drag, etc. and it might be possible for this version to do 20 kt with ~100 hp and 25 kt with ~150 hp. That is, if the weight can be kept down. I think it can be done....

This is of course not the only candidate for "next boat" status, but the others are too early in development and/or too unrefined to discuss yet.

 

OK, so Jeff tells me he's now allowing *.mov videos. Here goes.... the following clip is a smooth acceleration from idle up to approx. 9 knots true (20 knots model scale) speed. Note that the chop here translates to about 3-foot waves for the real boat, a condition in which trying to go 20-plus would most certainly get the passengers royally pissed off.

 

Matt, can't wait to see some sprayrails and a little development.

E

 

(just when you thought I wasn't paying attention...
Looking forward to some more shots Matt.... At speed there seems to be a fair bit of wave contact in the flatter aft sections - though as you suggest, one is unlikely to run at 25 knots in "rough" weather...the greatest advantage of a lightly laden boat of low deadrise is the ability to slow down to a speed that is conducive to the conditions.
Have you got any shots in calm water, or with the CG moved further fwd?

Just for your interest, I've started building a model of my own - slightly larger scale (1:1 )

 

You are making me very jealous, Will Big workshop AND big boat project? Paradise on Earth....

I haven't had a chance yet to test the tow model in calmer waters, or with accurate speed logging. The only navigable water nearby is Lake Ontario / Burlington Bay and it's hard to catch that at a calm time. Perhaps this weekend.... but thanks to a 55% jump in fuel costs since this design was started, with no signs of falling gas prices, this design is now in very tough competition with a hybrid/electric catamaran of similar size. (That boat is currently at the conceptual mathematical model stage and won't be an actual hull shape for a while, but it is looking awfully tempting... that's a matter for a different thread though.) Development on this one, in any case, will continue at a steady pace for a while yet.

 

Oh come on Matt...how many hours are you going to do in a year? 50, like most boaters...100 like the most regular ones? Even with higher fuel prices, I can't see the technological breakthrough that will turn boaters away from regular fossil fuels on the horizon yet - at least not at anything approaching a competitive price. And besides, you guys still enjoy some of the cheapest fuel prices this side of the dessert (as do we in Oz...though at $2.00 AUD per litre, it's certainly getting up there). The cost of fuel now is still less in % of average earnings than it was in the 70's, at least here...

Still, as you say, that discussion's for another place....

 

True, Will.... most boaters, myself included, simply don't use the boat enough to justify expensive, high-tech alternative systems. The good old combustion engine will be with us for a while yet, albeit in smaller and more innovative forms than we are used to seeing. And the skyrocketing price of gas does, after all, translate only into a couple of extra cents per kilometre on my Hyundai (9.3 c/km for fuel now, compared to about 7 c/km last year).

But this project isn't just about keeping costs down (although that's a major goal). It's also about thinking long-term, and about trying to do something that is different, that's not what you normally see. And, of course, about having fun in the process- both by designing something new and slightly unusual, and by ending up with a good, solidly built boat that is well suited to the task at hand. This boat will be around twenty, thirty years, maybe more; there is no rush to get it built right away (I won't even have space to do so for at least another couple of years).

One approach, the one being discussed on this thread, is to start from a planing hull and try to make it as efficient as possible in the lower planing and transitional speeds. The other approach I'm working on, ie. the aforementioned catamaran, is to take a displacement hull and push it way past the traditional fat-monohull problem of "hull speed".

The result will be two completely different boats, designed from two completely different perspectives, to serve the same purpose with the same crew in the same conditions. (This one alone has already spawned three variants, and I suspect the other will also develop into several related designs.) The decision as to which gets built (and what will power it- electric, gas, diesel, hybrid, nuclear fission, prop, jet, etc.) will be based partly on economics, and partly on which we like better- a decision that cannot yet be made.

 

Matt
Nice work. Test results seem a tad higher than Savitsky estimate. Will be interesting to see more definitive results with accurate speed and calm water.

I would be interested to see how chop affects power requirement.

I look forward to the next installment.

Rick W.

 

Well, testing for the season is probably over.... unfortunately I didn't get too many more tests in with the model (a combination of moving, doing some real cruising in a real boat, and assistants/family working weird hours or going on holiday). Other priorities are taking over now....

After spending some time in the probable cruising grounds of this boat, though, a few new criteria have come up that will have to be incorporated into the design:

- Efficient, no-wake running at 10 km/h, the speed limit on much of the Rideau system.

- Ease of access for people with joint problems, people carrying boxes of stuff, and large dogs (no terriers allowed). This boat will probably have to take on some occasional material-shipping duties as well as being a canal cruiser. Ever tried ferrying 100lb propane tanks, bags of cement, or structural insulated panels aboard a typical runabout? It's awkward, at best.

- Beefy, durable spray/rub rails and the ability to carry fenders normally found on substantially larger craft. Water levels on the Rideau, Trent-Severn and other canals are unpredictable and public docks are often in bad shape.

- The trailer must be able to launch the thing from a 5-degree ramp (non-paved beyond 1'6" deep) without a dock to stand on. The last four ramps I've launched Sunset Chaser from have all required someone to go in the water, and she's a long way from being a big boat.

More coming, eventually, once I'm done unpacking.....

 

A 26ft macgregor with all up weight of around 1800 kg can do 18knots with a 50 hp, and thats not a strictly power hull - so 20 knots with say 2400kg shouldnt need a 100hp one would think.

And a 28 footer should be faster for less HP.

 

The fact that the Mac26 can do that with so little power is indeed rather surprising. Indeed, that's one of the boats I looked at earlier in the design of this project. I personally don't like the Mac26, but it has some interesting capabilities.

*****
So an update on this project.... progressing rather slowly at this point, as it is now near the bottom of the priority list and will probably have to stay there until spring.

The "little" version of this boat- 8 m LOA, 2.0 tonnes loaded- is coming in at 64 hp (indicated) at 25 knots, 42 ihp at 20 knots by Savitsky method. A propulsive coefficient of 0.5 would thus suggest satisfactory performance from an engine of approx. 120-130 hp. The infamous, never-say-die 3.0 L straight-four comes to mind.

Still a few years away from being able to start construction of course.... but this has me thinking. For canal and inland-lake cruising, you don't need much in the way of onboard amenities; basically just a head, small galley and a dry place to sleep. The lockstations have everything else. So stepping down to the 8 m boat might not bring that big a penalty in terms of capabilities for the intended purpose. But at 1500 to 2000 kg, it would be much lighter (and thus trailerable with a cheaper truck) than the big one. And the move to the 8 m would also lop approx. 40% off the cost of the 10 m. Thus more likely to get built in a reasonable timeframe.

So.... any thoughts regarding how much cruising 2 to 4 people can do on a two-tonne, eight-metre boat? Tom Lathrop has convinced me that 2 people can do quite nicely with approx. 3/4 as much boat on some of the same waterways I like to cruise....