Starcraft Mariner '76 21 ft Splashwell modification questions

[jonnyfish]

I've done a lot of digging around the iBoats forums, and internet more broadly to really comb through what people have done regarding the giant splashwells on these older boats. I also know a lot of people's position on this subject: it's structural, leave it like it is - if you don't like it find a new boat.

While I understand that position, respectfully I would say "no". I love my mariner, for it's size, it's incredibly light, yet fights big chop surprisingly well, it also has high walls that i love in that big chop. I've ridden in mine enough now that I know I really don't want to make the switch. Instead - I want to better understand how to solve this problem - which is the splashwell.

Background:
I'm a casting fisherman, and having as large and open of a layout as i can for a rear deck is absolutely ideal. In my rebuild i'm looking to create enough seating space for 4 seats, and a reasonably rear casting deck. i understand I have a number of options here and I am exploring them (jump seats, fold up bench seat, etc. etc.)

Even so, the splashwell is a waste of space, and I think Starcrafts newer mariners lean into this with better designs that seem to use that space better while supporting the transom and walls.

So diving in, here's a snap of the back of my boat, with the transom and splash well, it's what you'd expect, standard from starcraft mariner in the 70s:


So with this, what I think i'm understanding is that the forces put onto the transom are also being absorbed by this really giant splash well. Not only that, but I'm understanding this splash well is also providing lateral support for the high walls, probably in part because the transom is so low? With these items my take aways are:

• The splash well must lend support to the forces exerted by the outboard motor on the transom
• The splash well must lend support to the high walls that are otherwise poorly supported.

Now, a question on the high wall support. I've noticed that through the hull design there are "ribs" of sorts that i interpret to be structural and lending support to these high walls. Is my interpretation of these pieces correct?



So with these observations i get into the harder questions. How can I create a simpler, more efficient, and equally effective splash well for my boat? I took a wander around the internet to see what other examples and options i could find as it relates to this boat and its splash well.

Here are some interesting observations.

Newer mariner splash well:
80s: (edit: i dug around more and realized this is not the same model, so not apples to apples)

90s:



It looks to me that over the years the incrementally fixed the design flaw that forced their need or a large structural splash well. I would be satisfied settling for the splashwell from the 80s. My question is, how could that be done in a way that still supports those high walls, is it the rib braces i mentioned earlier? I'm honestly curious in the picture i included from an 80s build how those walls were supported, unless that angled approach with the dip is sufficient support when paired with the ribs. If it is, great! I honestly don't see that as an overly complicated fabrication. I do note that on the 80s mariner there is a slight change to the transom shape, and the sides are thicker than they are on the 70s version of the transom.

Now, here's one that i thought was -really- interesting.

So, I have all the questions here. It appears to be a 70s style mariner transom. but there is NO splash well. Does this actually work? Is there enough support for the forces exerted by the motor? Are the bench seats providing support for the walls? I'm pretty skeptical of this but wanted to get thoughts anyway.

In general, I think a question I have is if I'm serious about this (which I very much am), is changing the shape of the transom board a requirement? Or am I in a safe enough place if I ensure that the forces that require support are accounted for (motor, and walls).

If I am off in some of my thoughts here please do tell me, but I'll be clear, I'm very determined to do this, I love my mariner and want it to be my forever boat. This is truly the most challenging piece to overcome in my rebuild.

 

[mattsteg]

It's not a Mariner or an outboard, but it is a 22ft Starcraft with a big, clear casting deck and seating for 4, so figured I'd post it.

You don't need your deck to cover a 350 small block like I do, but I don't see any reason you couldn't move the "support" piece down a bit and partially deck over the splashwell as it is...as long as you're ok with a high deck.

The transom I don't think transfers force to the splash well but rather it might support the sides. I don't have an OB to verify this.

 

[jonnyfish]

That's a cool setup!

You don't need your deck to cover a 350 small block like I do, but I don't see any reason you couldn't move the "support" piece down a bit and partially deck over the splashwell as it is...as long as you're ok with a high deck.

This has been my curiosity. If the splash well is truly in place to support the high walls, could i run a vertical support like the other rib supports i took pictures of, and then connect that support into a lateral support that is lower.

I'm really not sure, but at a minimum it seems like something that is worth exploring.

Ultimately i just really take issue with all the unused space of the splash well. I understand that I am using the boat in a way that it wasn't originally designed for - but losing like, 18 or more inches in dead space to the splash well is just frustrating.

 

[jonnyfish]

Here are some more examples I've found. This all just leads me back to - anything should be possible here - i just need to ensure things are properly supported. But i'm really looking for experience from those that have refabricated splash wells to maximize space or reamagine their boat layout

 

[mattsteg]

Yeah those old splashwells are hilariously over proportioned.

If you look at the splashwell from the rear - all the force is coming at the motor mount. The only support the splashwell would give against that torque would be via the tiny wings at the sides. It can't provide support elsewhere - the newer splashwells look more supportive of the transom actually. Any support is against the sides flexing in/out. You can probably just drop the crosspiece support a ways and be just as sound. The question is how much surgery do you want to futz with.

 

[Moserkr]

Not a mariner owner or an engineer but my .02... The main force of the motor is concentrated down low, and is braced by the transom to keel support piece (that I believe all starcrafts have. The splashwell is just what its called - a protector from water getting into the boat. Id have no problem dropping the splashwell down and condensing its size to just fit the motor. I would keep the supports running vertically from the hull to gunnel to combat flex. Adding a platform across the back would serve two purposes - combat flex and take some stress from the transom to the hull. Id tie in as much as possible for strength using angled AL and solid rivets everywhere if possible. You also gain some storage and use of otherwise wasted space.

Ive also seen people add the offshore outboard motor brackets to these hulls. If they can do that, the splashwell is a mute point. Just reinforce the transom where you make changes and put the platform in.

 

[jonnyfish]

Not a mariner owner or an engineer but my .02... The main force of the motor is concentrated down low, and is braced by the transom to keel support piece (that I believe all starcrafts have. The splashwell is just what its called - a protector from water getting into the boat. Id have no problem dropping the splashwell down and condensing its size to just fit the motor. I would keep the supports running vertically from the hull to gunnel to combat flex. Adding a platform across the back would serve two purposes - combat flex and take some stress from the transom to the hull. Id tie in as much as possible for strength using angled AL and solid rivets everywhere if possible. You also gain some storage and use of otherwise wasted space.

Ive also seen people add the offshore outboard motor brackets to these hulls. If they can do that, the splashwell is a mute point. Just reinforce the transom where you make changes and put the platform in.

This is great feedback and makes a lot of sense! I definitely feel like I have a path forward here, now I need to fabricate the new splash well.