Playing around with a 10 m trailer cruiser

From the research I have been doing on pumps, Id definitely go with the Ultra-style nacelles. That seems to be the ideal way to feed the pump, minimizing air introduction and offering a little extra lateral plane aft where it needs to be (though its pretty tiny). In the PNW, so many jet boats exist that are specific to whitewater that pumps seem to have taken a bad rap. Huge horsepower on heavy alu boats, bad fuel economy, and the stigma left behind by the go-fast big block jet boats of the 70s have eclipsed the efficiencies available with pumps. Im excited to see that progress as well.

Is the pump there for efficiency? Draft? If not for skinny water work, would a set of small skegs, possibly something at the sides of the nacelle, be the ticket? I know that its a trick of the fast boats to add small fins to the sides of the intake grate, and this would be an opportunity to add intake pressure as well as providing a bit of stability in what may be an inherent "personality" to the boat.

This shift is getting long....

E

 

In my case, the motivation for considering a jet is:
- Reduced vulnerability to damage (during high-water season, the amount of submerged semi-floating driftwood in some of these lakes is phenomenal- a prop repairman's dream)
- Reduced draught (beaching, for one, but also for the shallow and often uncharted rivers/canals I like)
- Reduced maintenance headaches (the relative simplicity and durability of a proper jet pump when compared to something like a Bravo-3)

In the jet configurations, I actually did end up playing around with the idea of small fins to either side of the intake after last night's discussions, as well as a few other forms of fin out near the chines. I'm not really putting much time into this aspect of it now, though, until I have a better idea of the true directional stability of the thing from the model tests.

One of those days, eh? Although I suppose in your line of work, E, a long boring shift means things are going pretty well in your town

 

Just a couple other thoughts to confuse the issue.

Looking back in this very interesting thread, I see that the Roughwater 29 and Lazeyjack's vessel on the trailer both have superb 360 visibility with the raised helm position, This can be sited over the engine box. A full height shower and head could then be accommodated in the cabin area to starboard alongside the helm, with access to engine from the portside passageway to the cockpit.

Guillermo's suggestion about the 200 hp Jetpac could still work as the unit supports much of its weight when immersed. Its dry weight is 422 kg or 930 lbs and Guillermo can advise you of the transom load in salt water. Watch the videos.

http://www.swordmarine.com/

The Tolman Jumbo can take 500 lbs on the transom and the Suzuki 140 seems to be the power of choice. The group has posted many examples of their work in building these Alaskan skiffs.

http://www.fishyfish.com/

Apologies if I have trodden on anyone's toes.

Regards,

Pericles

 

Sword Marine's JetPac certainly has the distinct advantage of not fouling up the cockpit with a massive honkin' motor box. It also has the advantage of being essentially plug-n'-play, almost like a large outboard, without the wire-by-wire rigging of an inboard. I will be researching this unit further.
What I'm worried about, in this case, is what adding around 200-300 kg (the weight that remains cantilevered after deducting the thing's own buoyancy) well aft of the transom will do to the trim at low planing speeds- even with the inboard it's proving tricky to keep the weight far enough forward. One of the goals for this hull shape is to reduce or nearly eliminate the "hump" and bow rise / stern squat when coming to plane, and to be able to cruise in that speed range if necessary. I have yet to reach a decision on whether to consider or reject the JetPac; that will depend mainly on how things look when I plug the unit into the boat's weights & moments spreadsheet.

 

The JetPac diesel can be rated 100, 150 and 200 HP, on the same basic engine. The higher the power the lighter the duty, of course.

Soon we'll mount in Vigo a 200 HP unit at the transom of a devotedly designed aluminim rib-like craft, for demo purposes (boat almost complete now). I'll post images soon.

Cheers.

 

Looking forward to seeing that in action, Guillermo!

*****

Below, some teasers of topside styling on the 8.5 metre version..... the cockpit sole, at 10 cm above load waterline, remains self-bailing and the engine cover forms a cockpit seat or table. Looks like 1500-1700 kg sitting at the pier and about 2370 kg at design load, for the current weights and moments table on this version. Those side windows on the wheelhouse would slide back completely over the fixed (opaque) segment to open up the cabin in good weather.

 

Matt,

The Tolman discussion group to which I belong is currently discussing the use of both the Armstrong bracket and 200 hp

outboards.http://www.armstrongnautical.com/repower.htm


----- Original Message -----
From: John
To: tolmanskiff@yahoogroups.com
Sent: Monday, December 31, 2007 12:18 AM
Subject: [tolmanskiff] Re: Outboard Motor Bracket


Neal,

We changed our plans in mid-stream. Before we glassed the bottom we
found out more information about the Armstrong type brackets and
decided then that is what we wanted. At about the same time we bought
a 200 HP Mercury for our power.

Ok, how do we go about adding an Armstrong bracket? I thought of
cutting into the transom next to the existing stringers so we could
sandwich the extensions about four feet. I worked all of the logistics
out in my mind and was about ready to do it......

But then I changed my mind again and decided to make the bracket out
of aluminum. Will start laying bracket and internal gussets and
brackets out in two to three weeks. The bracket will have flotation,
it will also have the hydraulic lift.

I don't know where to place the fuel tank, so the plan is to finish
cabins, flooring on the outside of the stringers, mount and set up
motor. Make a temporary floor between the stringers so it will hold
weight equivalent to a tank full of fuel (gearbox)for experimenting. I
will test boat with the weight distributed at different locations aft
and forward till I find the location for the center of the tank.

John

--- In tolmanskiff@yahoogroups.com, "skiffkits" <neal@...> wrote:
>
> John,
>
> Thanks for posting the bracket link.
>
> After reading the articles, a hot setup for a J24+ would be, build a
> 16-18" bracket built off extended stringers, (easily done, lt. wt.
> and strong) this would allow for added floatation between the
> stringers and a half or full width swim step and full ht. tranny,
> with walk-thru door(s) , if desired. Then use a 6" setback jack
> plate (preferably hyd.). This setup should be considerably cheaper
> than an Armstrong or other factory built full width bracket,
> especially when built into a new hull, it should give the same or
> even better performance results, as you'd have motor ht. adjustment
> on the fly for fine tuning and running shallows. If more forward
> tilt space for larger motors is needed you could use a 8"-10" set
> back JP instead of the 6", or build the bracket longer. Most
> brackets I've measured are 28-30" long to allow for full tilt range
> on the big motors (200hp plus). The Suzuki 140 can use a 24"
> bracket, transom angle must be taken into account too. With motors
> having to be mounted higher when a bracket is used the JP makes it
> easy to find the "sweet spot" and return to it, and with using a 25"
> shaft motor this keeps the power head higher for less chance of
> dunking.
>
> Careful consideration regarding wt. placement (fuel/water tanks
> etc.) would need to be allowed for during construction.
>
> I'm seriuosly considering going this route on my next build, which
> may start soon.
>
> Neal
> Skiffkits LLC
>
>
>
> --- In tolmanskiff@yahoogroups.com, "davewright112002"
> <usuallywright@> wrote:
> >
> > --- In tolmanskiff@yahoogroups.com, "John" <jklistof@> wrote:
> > >
> > > http://continuouswave.com/whaler/reference/engineBrackets.html
> > >
> > > We are going to add an Armstrong type bracket to our boat.
> > > http://www.thegearboxguys.com/boat.htm
> > >
> >
> >
> > Interesting article John, thanks for posting. It will be nice to
> see
> > how your boat works out with the bracket.
> >
> > To my particular prejudice, and it's only worth 2 cents, the
> molded
> > in bracket of the article made the most sense, i.e., you lengthen
> the
> > hull to whatever you desire in the first place, and shape the aft
> > section with step, or whatever other features you might want,
> > achieving everything a bracket may provide in an integrated "non
> add
> > on" fashion.
> >
> > But if you don't or can't plan for this ahead of time, then
> perhaps
> > the bracket is attractive.
> >
> > I liked the article's consideration of the downsides of brackets
> as
> > well as the upsides. The author seems to favor long extended
> > brackets, but I'm not sure that an objective weighing of the
> pluses
> > and minuses that he details would necessarily lead to his
> favorable
> > conclusion.
> >
> > In any case, you'll get a longer boat and the bracket will
> probably
> > meet all of your expectations and more.
> >
> > Best wishes to you for a successful installation and a heck of a
> nice
> > boat.
> >
> > Dave Wright
> >
>
---- Original Message -----
From: davewright112002
To: tolmanskiff@yahoogroups.com
Sent: Monday, December 31, 2007 3:01 AM
Subject: [tolmanskiff] Re: Outboard Motor Bracket


--- In tolmanskiff@yahoogroups.com, "nordski61" <enstad@...> wrote:
>
>....I have 60 gallons up against the #6 bulkhead and it's not too far
>forward. I don't have a big cabin so I can sure tell a difference when
>the tank is low on fuel. I had just 10 gallons in
> it the other day and really had to trim the engine in to get the
>proper boat trim......

Good info Aaron! I suspected this might be the case, but you're the
first Jumbo builder I've noticed mentioning it. I suspect that the
shorter the Tolman, the greater the bow up trim, and I notice it on my
18 footer.. I'm planning on adding a wedge to my motor mount this
spring to get more engine "in" trim for running up wind on breezy days.

This business is not unusual, and there're a number of boats that have
water ballast up forward for trim.

Dave Wright

------------------------------------------------------------------------

Matt,

The length of the Jetpac is only 50" on a 10 metre design and the longest Tolman Jumbo is about 25' 6", The Bateau DE 25 can be fitted with an Armstrong bracket as well. The videos at Sword Marine show RIBs jumping waves.

http://www.swordmarine.com/WatchItWork.asp

Addendum. From FAQs at website: The engine and water jet are both enclosed in a fiberglass shell, designed with enough buoyancy to fully support the weight of the complete unit, that attaches to the transom of a boat, like an outboard.

Elsewhere on this forum there have been discussions about powering boats onto trailers. I have a DVD showing the Jetpac boat doing just that, but without scouring the ramp bottom or damaging a lower unit.

Water ballast and judiciously placed diesel fuel tanks should take care of the hump, bearing in mind the good holeshot capabilities of water jets. I have purchased the Bateau plans for both the DE 25 and the LB 26. Whichever I build will have Jetpac power, especially as the LB 26 is an inboard.

http://www.bateau.com/studyplans/LB26_study.htm?prod=LB26

Good luck,

Pericles

 

Model test update

Just to prove that this thing hasn't died

The test model now has a deck and its first coat of fairing mud. It will take a few more weeks before it's all faired up and looking pretty. Towing brackets still need to be mounted- there will be one on each side (directly above the at-rest CB and with several tow points so that the towing force can be made effectively parallel to the thrust of the real drive unit) and one at the bow.

The towing rig will project out from the port side of my current runabout, keeping the model out beyond the tow boat's bow wave. I'm trying to figure out how to include a camera mount on it to get a video record of the tests. A scale factor of 0.167 means that the 2500 kg displacement of the 10 m prototype will translate to 11.6 kg in the model, which will use sandbags or other movable weights so that trim and displacement can be adjusted.

Since I don't have (or want to pay for) a digital speed log that is accurate in the 2-8 knot range in which the model will be towed, target speed will be approximated with the tow boat's speedometer and determined accurately by stopwatch over a measured distance (likely a floating line of known length stretched between two buoys).

I am not currently planning to use the model to evaluate hull resistance, although I may implement such a setup later. The model will be used primarily to evaluate trim, directional stability, ride quality and wake properties.

The tests will consist of back-to-back runs in opposite directions, at Froude numbers of 0.1 to 2.0. (Fr=2.0 equals 26 knots in the 10 metre LOA (9 m LWL) boat.)

Suggestions are welcome, as always!

 

Nice to see you're still progressing Matt.
Why not get hold of a hand-held GPS to measure your speed. It will be infinitely more accurate than your speedo, which in my experience are shockingly inaccurate at lower speeds. Your speeds will be over-the-ground as opposed to thru the water, but that is usually averaged over 2-way runs, and the effects minimised by selecting your test site carefully...

 

Dammit Will, now you've given me an excuse to buy another gadget. The electronics must be breeding or something; I'm already up to 11 digital displays of some form or another in this room alone.

I'm doing another fairing coat on the model tomorrow (yes, I know this is dragging out forever) and am starting on a towing harness. More to follow.
There's also a few mods to make to the tow boat... jacking the outboard up a bit (been meaning to do this for a couple of seasons but just finished fabricating the parts recently, and now have to take it to a welder) and some painting, among other things.
This is the great thing about small boats- all the fun of fixing up something big, without the rapid exodus of cash from one's wallet.

 

Congs for the improvements, Matt.
I had promised some images from the demo boat with the JetPac. Well, here it is at the Vigo Boat Show in March. Unit is a D200 HP and although the aluminium working boat is rather heavy for its lay-out and length (1200 kg w/o engine, 5.7 m open hull), we got 32 mph with 150 lts of fuel and four people aboard. I'll post more images of her in the water in another thread at the propulsion forums.

Cheers.

 

Looks like a good, solidly built craft, Guillermo. The photo really illustrates the advantages of the Jetpac over an outboard- nothing cluttering up the full, no-cutaway transom and nothing sticking down below to get caught on buoy chains, rocks, etc. I'll keep an eye on the propulsion forum for your sea trials

 

Latest renderings

Here's version 23 of the 8.5 metre variant. I'm trying here for more of an open feel while keeping the weather protection afforded by a full pilothouse. The wheelhouse in this one is down to just three panes of glass, but they're enormous- the single piece windshield is nearly 1.6 square metres. (Would probably be of acrylic or polycarbonate, as curved glass that size would be darned heavy and darned expensive.) The back of the wheelhouse has been opened up (canvas could, of course, be used over the cockpit in bad weather). Gunwale and spray rails have been changed to 2" aluminum extrusions after a closer look at some of the local docks.
Note that this version is laid out for a single sterndrive setup. Using the Volvo 4.3/DPS, it looks like it would come in a hair under two tonnes with full fuel and water (still working on cutting that down) and trim within a degree of where it should be at rest. (The boat itself is currently reading a bit under 950 kg, the engine/drive 420 kg, and the rest being tankage, batteries, gear, a grossly oversized anchor/rode, etc.)

 

Model test update

The 1/6 scale tow test model hit the water today. Not quite ready for action but it's getting close. Now that most of the pre-season work on the tow boat Sunset Chaser is done, I can focus on this again; I'm hoping to get some runs with it in June.

The model is 1.67 m LOA and currently weighs in at 13.20 kg dry. Each of the bricks currently in the engine bay is 2.30 kg. The model is slightly heavier than it should be when empty, and I am going to drill out some bulkheads up front to lighten it. With the ballast bricks in the stern, it sits pretty much level on its design waterline in the pool. (The nominal 3500 kg loaded displacement of the 10 m parent hull translates to 16.2 kg in this scale; with the ballast shown, the model is 17.8 kg, so it sits just a hair deeper than it should.)

The towing rig attaches to those brackets sticking out the side, which are roughly in line with the aftmost possible at-rest CB. This is similar to the setup Tom Lathrop came up with for testing his "Bluejacket". Tom's accounts indicate that towing from this point gives more realistic results than towing from the bow, especially when studying directional stability issues; my own calculations suggest he is correct.

(I should note, for the benefit of anyone else trying the backyard non-CNC way of doing this, that the glass-over-wood method used to construct this model is probably not ideal- the model is a bit heavier than it should have been, mostly because of the extra fairing that was needed with this construction method. For the next model I'm likely going with carved foam and a single-layer glass skin.)

 

Ok - I'm happy to be the bunny to ask the obvious question..... what's with the tennis ball?

And while I'm at it... how come everyone paints their tow models yellow?

Good work btw