Ideas For Cheap Fast Practical Trailer Boat

[Fred]

Motivated/distracted by Michael20, I now present a short list of attributes of a small boat to satisfy my urge to be on the water and urge to make things, to be constructed in 2 to 6 years time, unlike the other boat, which is more of a dream to realise, this is totally doable when ever I focus on it. IE, when FreeEMS is self-sustaining and/or nearly finished.

• 6 to 8 meters in length, the smallest that can do what I want.
• FreeEMS (petrol) powered, the smallest/lightest/cheapest setup that can push her fast enough fully laden
• Some sort of cabin at the front for storage and shelter
• Sleeps 2 up front comfortably enough (1.9 to 2.1m of bunk length)
• Front deck not a death trap IE, flat for walking/standing on, counter examples are easy to find
• A windscreen of some sort to shield the skipper from wind and spray
• Enough rear space for fishing and other activities, what enough is, I do not know, but can gauge as a I start to draw things.
• Constructed with foam sandwich, even if it's just cheap polystyrene and thin flexible plywood
• Ability to be driven onto a sand beach with no damage at low speed (prop and steering gear must be protected)
• Underfloor tanks for fuel only. Food and water and refrigeration etc provided by chillybin/cooler/icechest/bottled water/etc.
• Rear deck self-draining and/or sump and pump
• Unsinkable if swamped, IE, floatation chambers/blocks of foam/etc.
• 12V system for nav lights, instrumentation, engine starting, maybe some music, if so, two and isolation.
• Simple anchoring system, 3 to 6m of light chain, a fairly light style of anchor, and maybe 100m of light rope, terminated in a float capable of supporting all of it, such that it can be jettisoned to chase a fish in a hurry, or if carelessly dropped.

An automotive or motorbike engine in the 100 - 250hp range with an adapted cooling system would be suitable for use with a custom drive setup of some sort, perhaps creatively designed.

Hull Shape

My goals are conflicting here:

I would want it to be stable, ie, flat bottomed, but I would want it to be comfortable at speed, ie, deep V bottomed.

I would want it to be attractive, and efficient and comfortable into a seaway, but I would want it to be easy to construct with a lot of flatness.

Thought required on how to overcome this. Perhaps just learn to form foam cored sandwich around a shape and skip the flatness.

Deep V is OK with an outboard, but becomes a pain with a traditional drive line. Thought required to mitigate that, perhaps using $$$ to acquire a stern drive setup.

Fred.

[Fred]

It would also require a trailer built for it, that's no big deal though. Fully galvanised, for sure, as it will be taking regular trips into salt water. Single axle, possibly braked, possibly not, minimalist design. Maybe rollers, possibly skid load. Sealed LED tail lights for dunking.

[Michael20]

You wanted it, that it go's on

Yet i have started reading a big big Thread over, inboard vs outboard engine. First thought was inboard, but the outboard are running very great, and often more effienct as inboard Engines. The really advantage of the inboard is the price, because you could marinised it yourself, and buy the engine for about 1000€. Yes a new Outboard is fucking expensive. I'm Member in this Forum http://diy-community.de/showthread.php? ... yesterboot it's from a boatbuilder Master, that impressed me to build it myself sometime. And a friend of me has around 1Tonne GFK at home

Yeah 6meters is a fine lengh, so you could have a area to lie and chill

[Fred]

http://www.trademe.co.nz/motors/boats-m ... 082715.htm

That, but with a raised, flat front deck, raised rear gunwales, no hard top, and a different stern transom design.

Images cached here: http://stuff.fredcooke.com/challenger680hardtop7.2oa/

Fred.

[Fred]

Yet i have started reading a big big Thread over, inboard vs outboard engine. First thought was inboard, but the outboard are running very great, and often more effienct as inboard Engines. The really advantage of the inboard is the price, because you could marinised it yourself, and buy the engine for about 1000€. Yes a new Outboard is fucking expensive.

Yeah, exactly, a new or near new 100 - 250hp 4 stroke outboard is a LOT of money, enough to buy a cheap house in NZ... I'd be willing to live with the compromise to get a boat in the water and usable at a fraction of the cost of an outboard alone. I just have to figure out how to do it. I have an engine in mind, though, the KL-ZE Mazda V6, but that requires thinking about some sort of reversing box. If I went with a bike engine, I could retain the gearbox and possibly even get some extreme speed by shifting once on the plane LOL :-) Would make for an interesting experiment. If the experiment is a fail, the boat could be repowered and retransomed easily enough.

I'm Member in this Forum http://diy-community.de/showthread.php? ... yesterboot it's from a boatbuilder Master, that impressed me to build it myself sometime. And a friend of me has around 1Tonne GFK at home :)

Nice :-)

Yeah 6meters is a fine lengh, so you could have a area to lie and chill 8-)

For me it'd be about spending the night on it somewhere out at sea. And being able to move around in the cockpit while fishing with a bit of room to spare.

[Fred]

Perhaps my V-drive idea for the big boat could work nicely here too? Engine under a box in the back much like our old 32 foot boat had, and V-drive gearbox under the floor further forward. The hull shape could have a tunnel out of it to allow the prop to sit higher and still maintain some deadrise in the hull for cutting through waves smoothly. A small keel could be added to keep the prop safe, and a rudder or two behind it would work swimmingly. Hmmmm.

A couple of random engine box cockpit pics:










I could probably build a suitable V drive using parts from a 4x4 transfer case, too. I would/will need to find some sort of reversing solution if I use a car engine and not a bike engine/box combo.

Fred.

[Fred]

Design/construction likely order of events:

• Choose engine/gearbox/propeller/etc first.
• Design hull shape and front deck shape second. (already know what I want here)
• Add front V birth bunks for sleeping third.
• Engineer cockpit, decks, tanks, walls, doors, chairs, fittings, controls, windscreens, etc, last.

Hull shape depends on drive layout. Especially underwater and transom. Bunks must fit, so they are the priority with left over space after engine and anchor well. Everything else must fit into whatever space is left.

I might try to mock up a plan or sketch of some sort.

Fred.

[Fred]

Perhaps my V-drive idea for the big boat could work nicely here too? Engine under a box in the back much like our old 32 foot boat had, and V-drive gearbox under the floor further forward.

Yes, I'm certain it could now. I've been poking around and found a number of great little boats, mostly built for extreme speed, with exactly this arrangement.

A small keel could be added to keep the prop safe, and a rudder or two behind it would work swimmingly.

Yes, this would be awesome, not create too much drag, and really make the boat practical for beaches and other shallow water situations. If the rudder bearing system could support the full weight of the boat, then a skeg from the back of the keel to the rudder could keep the prop safe and everything happy. The strut could extend down to the skeg and support it in an additional place, too, if built strongly enough. I forsee building it from plate stainless TIGed together in a Y shape with the bearing central to the three arms. The tops of the Y would have a plate or two plates on them to mount to the hull.

I'd actually prefer to move the engine a little forward such that you could walk around the back of it equally to the sides. It could function as a seat with a squab on it, and/or a chopping board for fishing. The timber for chopping could be permanent so as to protect those seated from catastrophic engine failure.

I could probably build a suitable V drive using parts from a 4x4 transfer case, too.

I found someone that did something very similar to this indeed, and of course, he was a kiwi! His solution utilised two uni joints to make up the angle to the engine. I like this idea and it leads me to another point...

I would/will need to find some sort of reversing solution if I use a car engine and not a bike engine/box combo.

If I use a car engine (such as the KL-ZE) then I can also use a car transmission, complete with clutch and gear shift. A van gearbox could be used with a FWD gear shifter and cables. The factory drive shaft and uni joints could accompany it and be shortened to suit the setup if necessary.

For the prop shaft, I would need to come up with a way to support thrust in both fwd and reverse gears.

I really want to build a scale model of this now, but I'll have to wait to do that.

Fred.

[Fred]

Re keel and strut spacing and requirement for a bearing in between:

While there are formulas and graphs that can be used to determine bearing spacing, a practical rule of thumb often advocated states that there should be bearings spaced not closer than about 20 times the shaft diameter, and no more than about 40 times the shaft apart. In other words, a 1" shaft should have an intermediate bearing if the distance between the engine flange and the strut or stern bearing is more than 40". This figure in practice, however, is frequently exceeded. In any case, if shaft whip occurs, an additional bearing should be installed.

With respect to the keel length and end points, it will help the boat steer better if it's primarily in the centre of the hull, with the rudder at the back. Stopping it too far back will make the boat want to track straight more. In order to meet this requirement and meet the shaft support requirement, shape can be used.

The strut can also be shaped to move further away from the blades of the propeller while still providing ample strength.

http://glen-l.com/inboard-hdw/hdw-description.html

Fred.

[Fred]

Thinking about beam and length and proportions and suddenly remembered that I'd have to tow it:

The maximum width for a light simple trailer (including its load) is 2.5 metres (excluding side marker lights and direction indicators and the bulge towards the bottom of the tyre). An additional 25mm is allowed on each side of the vehicle for ropes, lashings, straps, chains, connectors and tensioning devices that are neither permanently nor rigidly fixed to the vehicle; or J-hooks (to secure stock crates or bins).

However I think it can be up to 3.1m provided the oversize parts are labeled as per the law. I'll have to research this more thoroughly at some point. A quick search reveals that the beam of most kiwi trailer boats is 2.5m, whether they're 6m long or 8m long... this is a clue. 2.5m it is.

Dimensions of K series V6 engine (L x W x H) 650x685x660 source: www.mazdamaniac.com/tech/SAE_20920677.htm (other good info on the engines too)

2500 - (2 * 250mm gunwales + 800mm engine box) = 1200 available, /2 = 600 walking space on each side, and the same across the back, which is still enough to walk in comfortably.

250mm gunwales can comprise of 130mm toe undercut, 50mm hull side thickness, and the 70mm balance in belting material, ample for a small boat. Thus with vertical sides, in-water beam would be 2360mm

Height for gunwales would be 700mm from the deck with 100mm of thigh support and 600mm to clear the top of the knee. Maybe 50mm more for top and bottom to clear the knee more. That's from the deck. The deck must sit above water level when fully laden and the overall height from chine to deck will be determined by the deck to water clearance and floatation required to keep the boat level. Cockpit will be self draining out the back through scupper holes with flaps.

The transom will not be flat, rather a significant curve will be put in it and it will lean backward too. This will aid in waves sloshing into the rear not breaching the edge and flooding the boat. It'll also keep the boat flat while reversing. A removable door will be present on one side or both sides for swimming and diving entry/exit.

Doing a preliminary layout with a few guesses it seems to me that I need to build it 7.4m long to get everything in as I would want it. This will mean a cabin/roof of about 2.4m, front deck of the same, and open cockpit of the same.

Construction via foam + thin ply + timber in places with appropriate bits of s/s and/or brass and/or alloy would keep it very light and fairly cheap, too.

Using a car drive train would keep the expensive marine stuff to a minimum.

This could work. I look forward to trying it :-)

My first roughly to scale sketch of the concept:







Some explanation is required:

• The inner of the two close lines at the bow is a mistake.
• The next bow shaped line is the estimated hull profile at bunk level.
• The two << lines are the bottom and top of the windscreens.
• The box in the middle of those is the steps to the front cabin, and standing area between bunks.
• The box in the middle of the cockpit is the 800x800 engine box.
• The squares and C shaped bits are seats, two rear, two forward, one for skipper, you can see the steering wheel.
• The line at the rear of the seats is the rear end of the roof
• The line at the front of the seats is a potential step up in the floor to keep it dry and safer from flooding.

Here's a photo of a similar looking boat, which I didn't realise this would be similar to until tonight. Except the propulsion, and front deck style it's looking to be virtually the same! :-/ That guy and I have very similar taste in boats. Similar background in fishing, too.

http://www.bluefixboatworks.co.nz/wp-co ... luefix.jpg

Fred.