Tri-hulled outboard motor boat

[JimD]

I'm building a mini one of these. Got two 8ft outriggers done and a 12 ft main hull started. Going to use a 2.5 Suzuki outboard for power. The motor will be housed in a covered well to minimize noise. What does everyone one think? (James, ol' friend, I think I already know what you think but feel free to comment anyway, if you like). Am using the small outrigger hulls I was going to use on a kayak to triak conversion that has since been abandoned. (The other kayak conversion continues but the amas will be much bigger)

Eagle 4.6 Trimaran

This head-turning powerboat is designed for fishing, or day trips in coastal waters.
The trimaran hull form has many advantages over a conventional monohull.The outrigger hulls make this boat virtually impossible to capsize, and allow the use of a very slender main hull, which slices through waves effortlessly. Because the hull is so slender, it does not need to plane to achieve high speeds, meaning only a small motor is required. An 8hp outboard will push the Eagle at up to 13 knots. The boat is suitable for up to 15hp.
The eagle can carry up to 3 adults, plus gear. There is a total of 10 watertight compartments making this boat virtually unsinkable, and very safe. The telescopic crossbeams allow the beam to be reduced to 2.4m for trailering.
Construction is from stitch and glue plywood, making the boat, simple, affordable, light, and rugged. This boat can be lifted by 2 people when the motor is removed.

Mine will not disassemble. It will be fixed with an 8.5ft beam. The hulls are all flat bottom and doryish. Just guessing on the weight but I'd imagine well under 100 lbs

[brucehallman]

What does everyone one think?

Just an aside, point of reference; Bolger designed a outboard trimaran called "Bantam". I recall that it was considered successful by the owners.

[botebum]

I fail to see any real advantage of this design over a low draft, light weight skiff.
Fishing would be awkward. It's too beamy to get into tight quarters. Getting in/out at a dock is a PITA.
A special trailer would be required or disassembly to cartop (which I've never been a fan of).

What do you plan to do with it?
What do you see as the advantages of this boat?
What am I not seeing?

Doug

[rbgarr]

If you didn't already have the amas would you still build this design?

[JimD]

If you didn't already have the amas would you still build this design?

Probably not. But I got 'em and this will put them to some use. Easy to stick a little sail on in sometime later, too.

[JimD]

I fail to see any real advantage of this design over a low draft, light weight skiff.
Fishing would be awkward. It's too beamy to get into tight quarters. Getting in/out at a dock is a PITA.
A special trailer would be required or disassembly to cartop (which I've never been a fan of).

What do you plan to do with it?
What do you see as the advantages of this boat?
What am I not seeing?

Doug

I don't fish. It will be beach and ramp launched off the back of a utility trailer I already have that is perfect for the job. I will use it for booting around protected bays. And since I already have the amas its at least half built before I even start. And I have no interest in any more monohulls. The future is in multi's, starting with this wee one. So from my point of view it makes a lot of sense. I can appreciate alternate viewpoints, though.

[JimD]

Just an aside, point of reference; Bolger designed a outboard trimaran called "Bantam". I recall that it was considered successful by the owners.

And I like this, too. Thanks, Bruce.

[rbgarr]

I'd just caution that you consider keeping your weight as low in the main hull of your new design as in the kayak setup they were designed for. The amas/outriggers might not support a 'higher weight fulcrum (?)'.

[botebum]

... The future is in multi's ...

I'm a huge fan of Multis. Not this one so much, but in general.
I love sailing cats as well as fishing off them. I used to pull my lobster pots with my 12' Aquacat. I've never been on a tri but the thought of sailing one turns the speed freak on in me.
I wasn't trying to deride your plan. I just didn't see the advantage of this design ... so I asked.

Doug

[brucehallman]

I fail to see any real advantage of this design over a low draft, light weight skiff.

I can't speak for the OP. (In case anyone is interested, otherwise please disregard), answering for the Bolger design Bantam 20/16 as I see it...

It has advantage of a roomy cabin for two people, with standing head room, that collapses down for easy towing by a sub-compact automobile. The three part hull was reported as extremely fuel efficient. I don't think that the same can be said for a skiff of similar displacement.

See this article for more description of Bantam 20/16.

[botebum]

I was speaking to the OP.
Comparing the Bantam to either the OP's boat or my suggested skiff is apples and oranges, better yet, apples and footballs.
I can understand your obsession with Bolger's designs (even though I don't share it in the least) but suggesting a Bolger designed cruising boat in lieu of the OP's boat just because it has three hulls is silly.

Doug

[brucehallman]

I can understand your obsession with Bolger's designs (even though I don't share it in the least) but suggesting a Bolger designed cruising boat in lieu of the OP's boat just because it has three hulls is silly.

I think you misunderstand me. I am obsessed with learning about boats by studying boat designs. Phil Bolger's work was published so prolifically I find it an easy target to study, but there are many others I study too.

And I disagree that pointing out the Bantam design being off topic. The thing shared in common between OP and Bantam is the hydrodynamics of the hull under power. Also in common is the issue of getting the thing on a trailer. I suspect that the OP might get a few ideas of the possibilities by studying Bantam.

Also, it is silly to dismiss Bolger's work in one fell swoop like you seem to do. The man designed 700+ boats over a very broad spectrum. It is easy to like some and hate some and have hundreds more to still to see without a closed mind.

[botebum]

Also, it is silly to dismiss Bolger's work in one fell swoop like you seem to do.

I have never dismissed Bolger's work as a whole.
I have stated many times on this forum that I like Chebacco.
It is true however that the majority of his work does not appeal to my eye or sense of proportion.

I will stick to my previous statement that you are comparing apples and footballs.
The only things the two have in common is the number of hulls and things common with boats with three hulls.
There are hundreds of other tris and proas that would be much more appropriate to compare.

That said,
Have a Bolgerific Day

Doug

[JimD]

I'd just caution that you consider keeping your weight as low in the main hull of your new design as in the kayak setup they were designed for. The amas/outriggers might not support a 'higher weight fulcrum (?)'.

Yeah, that is one of the things I'll find out about in a hurry. I originally conceived of this as a sailing tri whereby I'd be sitting on the windward rail but obviously that's not going to happen with a motor. Not quite sure what the volume of the amas are but they are 8ft long, 6" wide bottom at the widest point, a foot wide on the deck and close to a foot deep. No camera at the moment for pics. I'd guess they displace 2.5 - 3 cu ft, which is well in excess of my weight.

[brucehallman]

There are hundreds of other tris and proas that would be much more appropriate to compare.

I am having a hard time thinking of one other outboard motor powered trimaran than these two. I can think of a few catamaran powerboats, but tris? You know of hundreds? Goes to show I don't know everything.

[JimD]

I am having a hard time thinking of one other outboard motor powered trimaran than these two. I can think of a few catamaran powerboats, but tris? You know of hundreds? Goes to show I don't know everything.

Can't say I know of any others either. ...and to tiller steer this thing I think the motor can't be directly behind me. It will have to be exposed offset on a cross beam or perhaps the main hull could be offset itself, that is closer to one of the amas than the other. That way I could sit on the rail and still have the weight centered in the boat. Hmmm, seems odd enough to suit my style.

[JimD]

I'm a huge fan of Multis. Not this one so much, but in general.
I love sailing cats as well as fishing off them. I used to pull my lobster pots with my 12' Aquacat. I've never been on a tri but the thought of sailing one turns the speed freak on in me.
I wasn't trying to deride your plan. I just didn't see the advantage of this design ... so I asked.

Doug

Doug, I really don't know if there's any advantage to what I'm cobbling together or not, aside from it being a quick and cheap intro to multi's for me. I'm building a larger sailing tri which is also self designed. And I have no multi hull experience whatsoever.

[Woxbox]

One thing I would highly recommend is to move the amas forward. You want some displacement up there to keep the bow(s) from diving and tripping. To look at it another way, if a tri heels with the amas far aft, it will also pitch forward. (Like a tricycle.) Some of the bigger, heavier power tris do carry small amas well aft, but I can't see how it's a good idea in a small light boat.

At least three big power tris come to mind, all built to set distance/speed records. One of the latest is being run by that whale hugger bunch. The boat got a piece sliced off it by the whale hater types, but I think they fixed it.

Looks like a fun project to me.

[JimD]

Doubt if it'll be doing too much diving and tripping powered by a 2.5 so I was thinking the opposite, keep the amas not so forward to support the weight which will be mostly aft of center and I'm not sure if I'll bother trying to sail this thing.

[Wavewacker]

Well, if that's the only two, let's design another one!

How about starting with the Bolger Tenesse, @ 5' beam and 32' length. Let's have the cabin more like a trawler style with a cabin forward and a raised (somewhat) helm. Let's leave 10' aft with an open deck. 12' amas that disconnect and ride above the aft deck on a trailer, overhang is 2 feet. Can we get five feet in length at the rear of the cabin to "bump out" four feet to ride on top of the outrigging tubes? That would give you room aft for a queen bed with room to walk past. The other side "bumpout" could be a nice seating area and storage behid the seat (to hold the TV to be viewed from bed). Or, maybe the galley should be the furthest aft in the cabin with dinning on the other side, then the bed...whatever. Where is the best place for the head? Helm up front inside and a nice dash with a fold down table for charts and a lap top. Might have a hatch above the helm to jump out and run forward to throw a line.


Ah heck, let's throw a sail on too, guess the mast step would be in the head area or the galley wall?


Now, the amas, can fuel jerry cans go in there? Just to carry additional fuel.


Power with a 25hp outboard.


Anyone??? Is this doable???

[sailnstink]

Build it. Let us know how it works.

[JimD]

I'd like to put amas on one of these. Tastefully, of course:

[Wavewacker]

I think I'm being razzed a bit...LOL

Jim, I'd just like to have that boat!

Jim, how does your tri work, have you put a larger outboard on yet? Actually, I should try to build something like yours as all I have is the desire at this point. I'm not an engineer! So, something smaller would probably be more in reality for me. The Bantam would be a huge project for me.

[John Bell]

Well, if that's the only two, let's design another one!

How about starting with the Bolger Tenesse, @ 5' beam and 32' length. Let's have the cabin more like a trawler style with a cabin forward and a raised (somewhat) helm. Let's leave 10' aft with an open deck. 12' amas that disconnect and ride above the aft deck on a trailer, overhang is 2 feet. Can we get five feet in length at the rear of the cabin to "bump out" four feet to ride on top of the outrigging tubes? That would give you room aft for a queen bed with room to walk past. The other side "bumpout" could be a nice seating area and storage behid the seat (to hold the TV to be viewed from bed). Or, maybe the galley should be the furthest aft in the cabin with dinning on the other side, then the bed...whatever. Where is the best place for the head? Helm up front inside and a nice dash with a fold down table for charts and a lap top. Might have a hatch above the helm to jump out and run forward to throw a line.


Ah heck, let's throw a sail on too, guess the mast step would be in the head area or the galley wall?


Now, the amas, can fuel jerry cans go in there? Just to carry additional fuel.


Power with a 25hp outboard.


Anyone??? Is this doable???

Modifying a proven design as you've described above is just asking to make a very expensive mistake. Adding more windage forward on a shallow flattie like Tennessee will come to grief. It will sail so violently at anchor, you'll get whiplash. It will also be very hard to steer in a cross wind.

Bolger did design an 30-something foot folding trimaran motor sailer late in his life. But it's damnably ugly and quite complex. I have my doubts about how well it would work as well.

[JimD]

I think I'm being razzed a bit...LOL

Jim, I'd just like to have that boat!

Jim, how does your tri work, have you put a larger outboard on yet? Actually, I should try to build something like yours as all I have is the desire at this point. I'm not an engineer! So, something smaller would probably be more in reality for me. The Bantam would be a huge project for me.

Haven't got it built yet, my Wavy friend. And the rainy season is just about upon us here in the Pacific North Wet. There's lots of dead simple designs out there you could put together over the winter. Doesn't have to be a Bantam.

[Wavewacker]

Yes, Richard Woods has a long narrow craft with a tall pilothouse far foward and then drops to standing headroom and a nice aft deck, it's just missing the amas. The style needs to blend with a tri configuration IMO. A tug with outriggers would look a little strange. Richard's cruiser wouldn't look too good with amas just due to the style, arched windows and retro, it's very nice as is, but I'm sure it would rock......not sure about whiplash.

That boat would also be a huge project, not for a first timmer....


But a sleeker profile would work and blend with the tri concept I would think. I like the simplicity of the telescopic tubes but I'd like to be able to walk out there too....a wing maybe?

[JimD]

Yes, Richard Woods has a long narrow craft with a tall pilothouse far foward and then drops to standing headroom and a nice aft deck, it's just missing the amas. The style needs to blend with a tri configuration IMO. A tug with outriggers would look a little strange. Richard's cruiser wouldn't look too good with amas just due to the style, arched windows and retro, it's very nice as is, but I'm sure it would rock......not sure about whiplash.

That boat would also be a huge project, not for a first timmer....


But a sleeker profile would work and blend with the tri concept I would think. I like the simplicity of the telescopic tubes but I'd like to be able to walk out there too....a wing maybe?

There's a few simple small tri designs but if you're talking pilot house then you're talking big, expensive, time consuming. I've always found the aft pilot house to look best to my eye. A really skinny hulled version of Heather could make a for a unique tri:

[Wavewacker]

Jim, I can't really picture amas on that boat, flopper stoppers maybe, it's beamy and a very nice lines to her. But not as nice as that lady sitting on her deck!


You don't see her? Sitting on the northeasterly corner deck of the appartment building in the background in her PJs.



My ideal tri I guess would be a little sleeker profile.....