Stern Arrangements: What's Best?

[kmorin]

On the stern rebuild thread we've gotten into some discussion of the ways to remodel from a jet to an outboard engine. So that reminded me of one of my permanent smiles in welded boat building. How to design the 'best' stern arrangement for the outboard engine?

The stern of an outboard powered welded metal boat can be arranged in different ways and since we all have different ideas about the right way things should be…. Well we could, each of us, prefer one or another of those arrangements.
I’ve built lots of skiffs and so I’ve been involved in many people going around this decision cycle to decide which stern they like best? In fact I’ll be trying to show how we got here? What lead to the changes, and what thinking I’ve seen and what thoughts I’ve had on the subject.
I’ll start with a little stroll down memory lane and remind us all why things all started on the transom of the skiff? To tell the truth the real start was inside the boat, the outboard engine well, forward the transom needs a brief mention as well.
In each stage, I’ll try to remind us of the thinking the justifies that stage or design arrangement and to suggest what lead on to the next design evolution.

Please feel free to explain what I miss, to remark about your location and the experiences there, and to suggest other facets that I will naturally miss.

Disclaimer: I don’t intend to find fault with your opinion, I don’t intend to suggest that as a builder I’m any way qualified to suggest my ideas are better than yours. On the other hand I will probably poke fun at the logic and reasoning I’ve learned from others’ as they’ve explored this topic.

Let’s begin with outboards: they started out smallish. The 100hp, or as we now know 300hp engines were life time away when the initial small horse outboards first appeared. So they were light weight, not huge in size (compared to the original inboards) and reasonably compact. But they were also engines that needed tending.
Where to put them? On the transom, )I'm not mentioning the obvious fact these initial small engines were designed to go in this location)



So where did all this begin? Here, is a pretty little row boat made of dead plant parts, and pushed/pulled by more sticks of dead plants.



Now we're getting somewhere, the boat while very nice looking is still not made of metal except for the very new (we're talking history here not the model year of the kicker) power. No longer pulled or pushed by oars, and quite a bit bigger because of the ability of the new "engine on the transom" propulsion, the skiff is deeper, wider, longer and moves incredibly faster than any human can row the previous little boat.

What's next? (beside bringing in metal boats) Oh, forgot to mention the reasons to stern arrangements and here is where the history gets tangled. But first a word about outboard wells.



This little boat has the engine's transom inside the actual topsides and overall aft most transom- an outboard well. There are reasons for this arrangement, slow boats that don't plane, flotation aft the engine lifting the stern in a following sea, access to the early engines, and modern ones too if the skipper (as here) is inexperienced, and if you're fishing the wheel is below the bottom inside the bottom and out of the way of gear. All these reasons lead early builders, often building for commercial fishermen to install wells. Also the previously mentioned reliability of the early engines almost insured there was work done on the engine any give trip off the beach.

So we'll need to look back at the reasons for the first few arrangements but we'll do that next post.

Cheers,
Kevin Morin
Kenai, AK

[kmorin]

If you look at the dead plant skiff above; notice the outboard engine mount at the stern is cut down. The reason for this needs to be introduced as this will be a constant companion for the entire thread.

What's up? isn't that where the low point of the sides is? Yes.
Won't water come in around the engine? Yes.
So to put an outboard on the stern you lower the freeboard of an entire boat? Yes, if the outboard mount is lower than the sides and transom of the boat.

Let's recall that outboards are manufactured not built one off by craftsmen so they have standardized parts allowing the makers to cast and machine them in thousands to reduce per unit costs. That includes the aluminum castings of these engines' vertical drive shaft housing. This gets sort of confusing but; the original engines were very small horse power and therefore put on small skiffs where a 15" transom was decided to be standard which almost instantly was too low for the larger outboards of their day since they went on larger, longer, deeper boats.

The non human propulsion these originally smaller engines allowed boats to get bigger (bigger boat hauls more fish) but the manufacturers were a little behind the pace, so they waited until the demand for the next four inches of vertical drive shaft came from enough people before moving up to 19-1/2" transoms -at the time called a 'long shaft' but not to be confused with the much longer shafts in today's bigger engines. Profits were to be had with 18' and 20some foot skiffs that came about next but they had STILL little cut outs in the transoms- as the plank skiff above shows.

OK, now you're out fishing and really hit the mother lode, in your much bigger skiff than before, made possible by not rowing for 12 hours to go fishing. So the bigger skiff has a small outboard and to reach the water the stern is cut down because when the engine manufacturers first researched and sold the product they went on smaller boats with shorter transom heights. But now those low cut outs are really hurting the amount of fish you can haul with the bigger boats made possible by the use of these new engines and the increased amount of gear you're hauling, again, made possible by the reduction in rowing.

What to do? Well two things; first the engine makers need to make longer shaft higher horsepower models so the transoms of the bigger skiffs can have a taller freeboard, and that happened. But not overnight. The next step while waiting for manufacturing to catch up builders began putting a 'splash well' /slop tray/ safety box around the low point of the cut down transom.



Mostly this prevented waves that come in around the engine from flooding the entire boat, they just flood for a few seconds and drain out. The box that was added to the low point cut down transom because the engines weren't made yet with taller, longer vertical shafts, was an adaptation to the constant problem of having enough boats the same to allow engine makers to build for a given vertical transom dimension. So the builders had to build to the engine makers' dimensions.

But right away you can see that tiller handles attached to the outboard engine made the boxes have to get deeper, forward into the boat AND you had to reach down to hold them, bend over to fiddle with this low cut transom mounted engine- but it still beat rowing so the splash wells were accepted.

Engines got bigger and bigger and handling them with a tiller became more of a chore, plus the larger boats being pushed made it hard to see everything squating in the stern holding then tiller that was mounted so close to the water!

Cheers,
Kevin Morin

[paddler]

I'm contemplating a new build, a 24'-25' aluminum sport fishing boat with a pilothouse and cuddy. Most current boats of this type carry an OS bracket, which is a non starter for me. I want to maximize space efficiency. A splashwell design with a full height bulkhead will allow me to bleed my fish as I currently do. Eliminating the common transom fishbox will increase cockpit space and make it easier to fish around the engine. The problem is that self bailing decks restrict the space for batteries, switch, ACR, fuel filter/water separator, etc, under the splashwell. One solution to this problem would be using the Optima batteries, as these could be mounted lying down with the terminals facing forward. Another possibility would be to raise the outside corners of the splashwell to accommodate standard batteries. Anybody seen this done?

[Chaps]

I spotted this one a few years ago and thought that if I ever had a splashwell boat built I would do it something like this one. I like the fact that you can stand in the aft corners of the deck, the chances of water coming in the boat are nil and fishing around the engine is as easy as it gets. Additionally, to address paddler's issue with having batteries and switches jammed into the bilge under the well, in this case the batteries are in the bump-out hatch in front of the well and are at deck level so are easy to service. The bump-out could be as tall as the splashwell bulkhead to create a tackle center, fish cleaning station or a livewell.

[paddler]

Yep, I've seen that arrangement as well. My current boat isn't self bailing, so it's important to keep blood and slime out of the boat. A full width splashwell helps with this, as you can bleed fish in it.:



Of course, you could do a combination of the two.

[jj225]

With that setup might as well be an I/O IMO. It doesn't seem to be all that much space saving compared to the more common models of full transoms. Personally I'm not crazy about the cut out version. Know of boats that have been swamped/sunk due to waves coming up and over especially on the hook. Lee Shore makes a boat that Paddler is describing. Think Crozier does as well.

[kmorin]

Thanks for the posts AAB'ers I'd hoped to get at least some feedback.

here is the next evolution and its being talked about already so it has some following.


The full width splash well or slop tray as some call it. The idea simply takes the cutdown transom's stern protection bulkhead around the engine and instead of making a three sided surround, thanks for the images Chaps, those are perfect for the discussion.

The idea here still keeps the engine mounted to the transom of the original boat hull length, it still keeps the lowered cut down safe in a following sea and as paddler notes, works for other purposes too.

But... as noted, it does take up deck space and the bigger the power head the farther forward the well/tray/false transom has to be. So a 100+ hp engine starts to need 27-30" of deck space depending on the rest of the geometry of the stern that is 2 feet of deck, given up to the engine's design and mounting and the resulting hull protection of the surround.

What to do? The deck of fishing boat, commercial or recreational is some expensive real estate. The deck is where the action is, so the entire boat could be described as a means to get this deck out to the fish and back in whatever weather comes along? I know that is oversimplifying a bit but really think for second about what the deck is? It is the reason for the boat in many cases. The deck is where the fishing happens, the deck is where the fisherman fishes so.. back to my original statement the deck is about the most premium value in the boat if she's been built to haul you off shore to fish.

Say the boat is a 24'er with about 1/2 helm/cabin and 1/2 deck. (it's usually much more like 5/8's cabin) Then she might have as much as 12 feet of deck (multiplied by her beam for area)? but the engine to push this boat HAS to take up 30" leaving 9'-6" where there was 12'- the engine takes up 1/5 the boat's deck! that's some serious area of the purpose of the boat given up to the fact outboards are manufactured with too short legs, and unchanged stern mounts for too long! For every boat that is not 50% deck space and instead has a larger ratio of cabin to LOA; the amount given up by these initial stern arrangements goes to a higher percent of the premium fishing space.

What can be done?

Cheers,
Kevin Morin

[kmorin]

Outboard racers know that the farther aft of the center or gravity of the boat they can place a mass the potential faster their boat can go. So a big mass is the engine, and it could be hung off the stern of outboard racers using a metal or even cast plastic bracket.

I'm not sure who started this, but the Gill Bracket was one of the first widely recognized products to be bolted to a boats' transom so the shape of the hull could remain full height of the topsides all around the hull, AND yet still accommodate the engine mounted to the stern. There were, and probably still are, many of these engine cantilever bracket products around as they did their job to move the engine aft, improved performance a bit and solved the loss of deck space to the previous engine mounts shown above.



Notice the bottom surface of this cantilever box? Some of these frames were not boxed in sheet metal but were just pipe frames with a little plate to bolt the engine mount on. I show the version where the entire cantilevered bracket is of plate.

The lower surface is not at the bottom of the boat, was most often completely free of water when the boat ran on step (planing) but some of these brackets with the bottom surface as shown, DID add to the positive displacement of the stern when the boat settled off plane and sank into the design waterline at rest.

So the Gill bracket (that's probably a trade mark? so I'm using it to describe an entire series of product and my version is just for illustration) solved the deck space loss problem while improving top speed as well as improving steering by putting the wheel aft the hull a couple feet.

then what?



Some one noticed that the Gill bracket's lower surface could be used to help with planing the hull! That is- if the formerly upward slanted bottom surface of the bracket were to be fabricated to the existing plane of the bottom surfaces, shown above, the bottom of the boat would become longer and when at rest the bracket would add some more flotation to the stern by displacing more water.

The engine is still aft the hull, the transom is still full height to the topsides height, the running speed is increased by the location and there's really nothing you can do to a modern engine at sea- so why bother to have it close inboard where you can "work on it" ?

So we've gone from open stern cut down mounts to transom mounts with splash wells around the low point to brackets and now short narrow bottom extensions doing all the jobs of the previous arrangements as well as getting the full deck space back for use.

What happened next? Well swim platforms or small side decks could be added maybe?

Cheers,
Kevin Morin

[kmorin]

With a small amount of plate filling in the two open corners of the new stern extension outboard bracket we could have some MORE deck space.
This is some expensive real estate and getting a low cost addition to this expensive commodity is worth looking closely at the details.



Here are a pair of metal squares/rectangles shown outboard the central hull extension 'bracket' that holds the outboard. Since the extension is there already, it provides 50% of the support and structural stiffness required for this 'deck extension'. The transom is the other 50% support and a small amount of metal goes a long way because the two supporting structures were already afforded, by the previous decision to extend the hull for the engine.

So the next variation in a stern arrangement is to flank the engine's center hull extension with flanking plates that are used for all sorts of good and benefit the boat's overall utility. They allow boarding over and through the stern, formerly not even considered, they allow gear to be carried lashed on the stern, coolers and buoys, anchors for gear and lots of other equipment find a handy home on the steps aft.

We need to review and look at the progression in a single image, so I'll line up these various stages of arranging sterns (evolution of design) so we can make a visual comparison of the steps so far.



Here's a look, left to right, coming toward the foreground are the different basic ideas we've seen that are employed to arrange the engines on the sterns of welded boats.

What happens when you need two engines instead of one? Well the central hull extension has to be a little wider, that may be true of adding a kicker too? Some kickers we've seen can be added to the sides of the swim platform or cantilever deck panels to the sides of the main hull extension but many times the central extension is made wider too.

Cheers,
Kevin Morin
Kenai, AK

[paddler]

Crozier tells me that a cuddy will take minimum 80", but I think that's low. The helm requires about 44", plus passenger seating behind that, figure 48". The splashwell will take 30", as you say, or even a bit more depending on the engine. So that total is 202", give or take. The cockpit deck is whatever is left over. In a 24' boat, that number is ~7'. I'd guess it's really closer to 6', and a 7' cockpit probably fits better in a 25' boat.

Kevin, you give a nice summary of the development of the brackets. The Armstrong was just welded pipe bolted onto the transom. Ranger claims credit for producing the first integrated bracket, I think back in the early 80's or even the 70's. They called it a "high performance engine setback". It's important to realize why these brackets were developed. The bolt on type really did free up deck space for a given hull. You have a 16' boat, just bolt on a bracket and you increase usable space. The elevated bracket by Ranger improved top speed by reducing wetted surface area, and important consideration for bass boats where hole shot and getting to a spot first means you get to fish it and late arrivals have to give you space.

Times have changed, though, at least for fishing boats intended for use offshore. Most of the so called Offshore Brackets are now full width extensions of the hull. One could just as easily view current brackets as hulls with the sides removed, in other words, a negative space when compared to a full hull of the same LOA. The 24' North River O/S is really close to 27' long, for example. I've had this discussion many times. My own view is that there is very little cost or weight savings to be had between a bracket or a full length hull, and the latter has more usable volume.

[speedboats]

The problem with making the 'cantilever box' an extension of the keel line is that it moves the centre of lift forrard when on step, essentially negating the aforementioned advantage on moving the large mass of the engine aft.

I guess what you are moving towards is that as more weight gets hung off the transom (7 Marine do that behemoth 6.0L V8 outboard), and folks want to stand in the aft corners or on the platform and fish / work, then there is a requirement to add buoyancy to those aft corners, so you end up with a longer boat that is essentially the 'Three sided' or 'Full width' splashwell'.

I guess it's kinda like how we call bellbottoms 'Boot Leg' now. Or in the words of Tommy Lee Jones in 'Under Seige', "Welcome to the revolution man, so called 'cause everything keeps coming 'round..."

[treedoc]

Hi all, been lurking from NZ for a while now..

Thoughts on this transom arrangement?
I believe the hull was retrospectively extended to under the transom steps to accommodate the weight of the 115hp on this 5m hull.
The pod does not extend down to the keel line.

I am having the same boat built and have the option for the hull extension, although I am putting an 80hp Suzuki on mine.

We have some fantastic alloy boat builders in NZ, they are very popular and often command a price premium.

[paddler]

Boat.jpg

Hi all, been lurking from NZ for a while now..

Thoughts on this transom arrangement?
I believe the hull was retrospectively extended to under the transom steps to accommodate the weight of the 115hp on this 5m hull.
The pod does not extend down to the keel line.

I am having the same boat built and have the option for the hull extension, although I am putting an 80hp Suzuki on mine.

We have some fantastic alloy boat builders in NZ, they are very popular and often command a price premium.

The maximum flotation at the stern is, of course, a splashwell design in a full hull. Static trim is a consideration, but if you have the option, I'd opt for the full hull. In this case, you'd end up with what's called a Euro transom, which I think flows well and looks good.

[kmorin]

OK, "back in the saddle again" with a few minutes to update our images so we can keep looking at the strange evolution of our welded aluminum outboard engine powered boats.

First its was.... oars and a rag with a stick to hold it up; then
transom mounted engine, open at the gunwale; then
cut down transom because the sheer went up because we could haul more with an engine in the second iteration; then
to keep the sea out a splash well/slop tray/ but not a hole in the hull 'well' which is more branch on this tree than trunk; then
a deeper fore and aft well to accommodate longer tillers, bigger block heads and more engine; then
a full width well/tray/splash bulkhead -but it began to "give up" more deck space to the engine mount; then
the first bracket to get deck space back, get more speed from existing power and give more room in the cockpit;then
might as well get some floatation once the bracket began to be plate instead of pipe; then
Well! some decks along side the " bracket that floats" is only a few pieces of plate and the support is already there; then

So, designs have progressed logically as each step is only a few pieces more metal, and a few hours labor. Not a new hull, not a significant adder, just incrementally increased within reason to the whole project.

As mentioned last post the idea that's next is....
"Say, if I had two outboards instead of one.... I could put them both back here!"; then



What we have here is a just a small width change to the previous flotation and planing bottom adder bracket, that holds to engines. Maybe its wide enough for two and a trolling motor/kicker too? ( I added some green panels to show the original width bracket widened to starboard ONLY)

But then.... what's next? Well, logically a little more metal could make the side deck/swim platform more secure and we can put lockers, totes, tanks/ or coolers out there to clear out the deck!

So! what if we put wings or sloped topsides extensions on the sides of the swim platform/side decks/stern platform: then



The keen eyed AAB.com Forum reader will see that I didn't use the 'widened' float hull extension type to put the side 'wings' on but the ideas is that this is the next piece of metal that can be easily added to perhaps improve the look of the stern extension, to give some sides or coverage to the deck and to help with support is the deck will have totes/tanks/coolers for loads.

But now that there's a bracket about 2/3's the beam fit to the bottom and the boarding platform full width, with some of the sides added in: why don't we just fill in the bottom? I mean the plates are only a few square feet and the rest of the boat is all but "there"; then



Here's a full width bracket with 'wings' and a deck room for two or a big single and plenty of room for trolling motor, kicker and some coolers or tankage. Now we could reasonable put hatches in the top of the deck and make stowage, lots of room here, full flotation and its completely reasonable to add watertight hatches to this serious bit of construction; right?

So where do we go from here? I mean this is a progression of thought- at least it was for me when I was building full time.

I'd say we're getting close to the 'ultimate stern arrangement'. Its helpful, I think to recall the stages we went through to get to this design evolution. Just start at the top, review the various drawings and see where it leads?

Cheers,
Kevin Morin
Kenai, AK

[kmorin]

Now to get to the final ultimate design!

Next is to add more to the wings so the sides are full to the sheer!; then



We only added a few pieces of metal and just filled in the topsides from being wings to being the full side ht again, I mean there's just a little metal and a few hours, nothing major here.

Where will we go next? I hope its getting clear to everyone, where we came from! But the reason is to get deck space along side the engine, and we've added a full 2' to 3' of deck by going through all the stages up to here- why not just box off the engine in a splash well and have that space as deck??



BUT WAIT, you say? that's sort of like the begining of the transom mounted engine with a well and splash guard????? wha'ts up...
That's right and let's compare the two shapes.



I admit that the colors and transparent panels in the middle model are there to show the step by step additions and incremental planes of metal we added but when we're done with this stage what do we get? Well there's one to the left of the step by step model in the middle and the one on the right just shows those same panels in one color like the original.

Now what was our thought process? Let's review in an image summarizing the steps we took, all logical, all for a good reason and all incrementing the idea of the next design stage is "just a few pieces of plate and little welding" along the process of improving the stern design in ALL welded outboard skiffs.



What can I conclude from this historic design exercise?
First there a several ways to mount the outboard engine on any given skiff, and when they are followed to the end of the logical sequence they simply extend the hull and then begin again.

Second; what can we do to improve this splash well design we ended up with? I think we could move the engine aft on a bracket... don't you?

Third; Any stern arrangement you want is fine, they all have reasons, they have followings, they all work, they all fish, they all come home. Its your' money, get what you want in YOUR stern design.

So for the mental health of your builder just pick a length and the stern you like best and hush, stop & write the check and enjoy your boat. Please don't try to 'rethink', 'out think', 'think trough' or otherwise add your wisdom to improve someone's design.

If you need to do that? Please learn all the skills needed to design your own boat, and build it 'your way' which is the best way, of course.

the humorous thing here is that if someone took my advice, learned to build, and then designed and built their own; inevitably another (2nd)individual, sometime will approach them to build another skiff for that 2nd person. AND when the two begin to discuss a new prospective design that 2nd other person will say:

"Now: to improve your stern design....."

Hey AAB.com Forum, in my experience the first couple hundred welded aluminum boats are an extreme education in people, business and barnyard expletives so I hope you will be able to smile with me at our sometimes confusing follies as we seek the best boat or our dream boat in welded metal.

now if I just added a little plate here.....

Cheers,
Kevin Morin

[Chaps]

I like your final conclusion Kevin, looks just like the dive boat I posted above.

An alternative to a fixed bracket attached to a full height transom is to use a porta bracket. It gives a nice setback for more efficiency and quick planing, allows incremental adjustment up and down enabling fine tuning of motor height for load, provides a means of getting the entire engine out of the water when moored, allows safe, slow cruising through shallow water by lifting the engine vertically until the prop is higher than the keel, provides full hook-up of the prop in rough conditions by dropping the engine deep enough for the lower unit to be in clean water all the time, etc. and never any water coming in over the transom. And its a simple bolt-on solution.

[paddler]

Kevin, your tracing the evolution of the bracket is the most complete explanation yet of what I've been saying for quite some time. Extending the full hull by the length of the bracket yields more usable space, better transom support and more engine flotation than a bracket boat of the same LOA. I prefer a full width well because it provides a nice place to bleed fish, but that's a minor difference. I like the Euro transom look, but would flatten the aft angle of the sides. Doing so means the transom would be cut out where the engines mount rather than extended. It may be hard to picture what I'm talking about and I don't have your computer skills, but maybe some will understand what I mean. You can get an idea looking at the photo I posted previously.

Adding a bracket to a splashwell design, then filling it in, then adding another bracket, then boxing it in again seems a bit like a dog chasing it's own tail.