2006 Hunter 25 - Swim Platform Stress Cracks

[robm]

Happy Friday before Labor Day.

Update 1: Fri, 9/2, 3:30 PM EDT - Modified to reflect recommendations by @Ralph Johnstone in the post after this one. Changes marked with ETA1. When I finally start the job, I will document what I did and add a new post for the procedure + result.

Thanks for the call yesterday, @Crazy Dave Condon; appreciate your time, expertise, and stories. I'm going to focus on the motor mount, motor support, and motor angle suggestions this weekend. Will follow up on the other suggestions after that.

@Ralph Johnstone, finally had a chance to open and assemble the Extreme Max transom saver. It's solidly-built. Am going to dry-fit it to see if it can support the motor without movement when tipped forward / up. Will take photos and report findings. Still open to removing the motor for transport and storage during the offseason; am thinking the transom saver would be nice to use during the season when the motor is installed and the boat is on the trailer.

Re: the current repair plan for the motor mount, see below.

Update on what I have on hand for metal stock:

• Aluminum: 2w x 1/2d
• Aluminum: 3w x 3/8d
• Stainless Steel: 3w x 1/4d

I have 10+ feet of each of the above. Read on for what I am thinking for a short-term motor mount repair to get me to the end of this season.

Backing Plates

• Seems like the 3” aluminum would be a good choice for replacing the motor mount backing plates, mainly because it will be much easier to machine onsite.
• Backing plate sizes would be 3" x ~13" for the starboard (outer) motor mount bolts, and 3" x ~15" for the starboard inner motor mount bolts. These sizes would span the entire underside of the flat section of the transom / swim platform. I believe this should stop all of the flexing if the backing plate is fastened with a proper adhesive (see below). ETA1: Per @Ralph Johnstone's suggestion, I am going to orient the new backing plates from port to starboard (was originally planning to use the fore/aft orientation with wider longer plates). Will update the plate lengths when I take new measurements.
• Will use my friend’s milling machine to round all four edges of the transom side of the backing plate using a corner rounding end mill with a radius between 5/16 and 3/8 (I'm working from a photo he sent me with a tape measure behind the end mill).
• I can replace them with larger plates during the offseason, if the sizes I specified don't stiffen the horizontal transom section sufficiently. ETA1: This comment has been deprecated; the port/starboard orientation should be a proper fix.

Hardware

• Existing bolts seem fine. Will remove them, clean them, and reuse them.
• ETA1: For the new plates, will drill and through-bolt with washers and stop nuts.
• ETA1: Will use Loctite 567 for the bolt/stop nut connections.
• ETA1: Will use a suitable non-silicone sealant for the bolt/motor mount/transom connection.
• Existing motor mount backing plates are tapped. I could tap the new ones after drilling them, or just through-bolt with washers and stop nuts. Open for suggestions.
• I have Loctite 567 thread sealant on hand, but could use a marine sealant for the bolts. Open for suggestions.

Installation of New Backing Plates

• For bedding / attaching the new aluminum motor mount backing plates to the underside of the transom, I'm thinking Loctite Marine Sealant after reading Practical Sailor's marine sealant review: Marine Sealant Adhesion Tests - Practical Sailor

Removal of Existing Backing Plates

• @Crazy Dave Condon said that the current backing plates likely used 5200. This is likely to present the biggest challenge re: performing the repair this weekend, given that I am having trouble locating a local source for an appropriate debonder / remover for PU adhesives / sealants like 5200.
• ETA1: Given the change in orientation for the new backing plates, I no longer need to remove the old backing plates. Instead, I will cut/grind/scrape about 2" of backing plate and 5200 from the end of each existing plate to make room for the new ones.
• ETA1: Turns out I had some
• I ordered a bottle of Re-Mov from the vendor, but it won't be delivered until next week. ETA1: This will be handy to have on hand, but it looks like I won't need it this weekend.
• If I am up for the drive, I can get BoatLife RELEASE from Jamestown Distributors today. It seems likely that this is what I will end up doing. ETA1: Today I learned that Jamestown Distributors no longer has a retail store at their distribution location, which means the days of same-day pickup have come to an end. If I end up wanting BoatLife RELEASE, will have them ship it to me, but it's not needed this weekend.

Pausing here; need to hit the road to procure supplies.

ETA1: No need; had everything on hand after reading @Ralph Johnstone's update!

Rob

 

[Ralph Johnstone]

Seems like the 3” aluminum would be a good choice for replacing the motor mount backing plates, mainly because it will be much easier to machine onsite.

Agree, good choice.

Backing plate sizes would be 3" x ~13" for the starboard (outer) motor mount bolts, and 3" x ~15" for the starboard inner motor mount bolts. These sizes would span the entire underside of the flat section of the transom / swim platform. I believe this should stop all of the flexing if the backing plate is fastened with a proper adhesive (see below).

I understand you will be installing the new backing plates at right angles to the original plates. Faaaaaaaar better than the original orientation of the plates.

Will use my friend’s milling machine to round all four edges of the transom side of the backing plate using a corner rounding end mill with a radius between 5/16 and 3/8 (I'm working from a photo he sent me with a tape measure behind the end mill).

WOW ! I'm OCD but you're a bloody perfectionist !

I'd use an angle grinder to eliminate the edges on the tight corner fits against the vertical transom. I'd be more concerned about the tight fit shown below:

Remember, the only forces of any consideration are the vertical upward forces and they only occur on the forward flat bar. For the most part, these will be greatly reduced.

Existing motor mount backing plates are tapped. I could tap the new ones after drilling them, or just through-bolt with washers and stop nuts. Open for suggestions.

Through bolt only for ease.

I have Loctite 567 thread sealant on hand, but could use a marine sealant for the bolts. Open for suggestions.

Sounds good with low strength Loctite.

For bedding / attaching the new aluminum motor mount backing plates to the underside of the transom, I'm thinking Loctite Marine Sealant after reading Practical Sailor's marine sealant review: Marine Sealant Adhesion Tests - Practical Sailor

Adhesion is of no interest as the nuts supply continuous compression. Something good and thick which will stay in place while wet. With the 3" wide material, you have a very large surface area which will absorb any large forces which may be encountered. Far easier that resin or epoxy in an overhead location. Tighten slowly once everything is in place to ensure all air bubbles are removed as sealant oozes out.

@Crazy Dave Condon said that the current backing plates likely used 5200. This is likely to present the biggest challenge re: performing the repair this weekend, given that I am having trouble locating a local source for an appropriate debonder / remover for PU adhesives / sealants like 5200.

Use a grinder as you're only taking out four (4) 3" wide sections at right angles. Old plate can remain.

I ordered a bottle of Re-Mov from the vendor, but it won't be delivered until next week.

Don't think it's needed at this time.

If I am up for the drive, I can get BoatLife RELEASE from Jamestown Distributors today. It seems likely that this is what I will end up doing.

Any Marine sealant would be good. Also, this isn't seeing any water so just about any sealant is good. Again, the 3" wide backing plate is presenting a very large surface area to absorb force. This in turn is transmitting that force to a much larger FG structural surface area than was previously presented by the poor orientation of the first backing plates.

This is more than sufficient for the reinforcement of the motor mounts. Maybe keep the following in mind to avoid repeated cracking:

2. Grinding out the damage in the FG and refilling with whatever is required depending on the depth of damage. I would do it without the SS support in place to ensure no stresses added to the FG and no future cracking of the repaired gel coat.

Final gel coating can be done down the road.

 

[robm]

@Ralph Johnstone, thanks for the detailed response. I updated my previous post to include your suggestions.

I understand you will be installing the new backing plates at right angles to the original plates. Faaaaaaaar better than the original orientation of the plates.

I hadn't been planning to do this, but as soon as I read the above and your subsequent comments, I was 100% on board. Great suggestion!

WOW ! I'm OCD but you're a bloody perfectionist !

I'd use an angle grinder to eliminate the edges on the tight corner fits against the vertical transom. I'd be more concerned about the tight fit shown below:

View attachment 208936

Remember, the only forces of any consideration are the vertical upward forces and they only occur on the forward flat bar. For the most part, these will be greatly reduced.

Haha, I'm a reformed perfectionist, but can be functionally just OCD enough when good engineering or labor-saving options call for it!

Through bolt only for ease.

Sounds good with low strength Loctite.

Adhesion is of no interest as the nuts supply continuous compression. Something good and thick which will stay in place while wet. With the 3" wide material, you have a very large surface area which will absorb any large forces which may be encountered.

Sounds good! Updated my post with the above.

Far easier that resin or epoxy in an overhead location. Tighten slowly once everything is in place to ensure all air bubbles are removed as sealant oozes out.

Any Marine sealant would be good. Also, this isn't seeing any water so just about any sealant is good. Again, the 3" wide backing plate is presenting a very large surface area to absorb force. This in turn is transmitting that force to a much larger FG structural surface area than was previously presented by the poor orientation of the first backing plates.

This is more than sufficient for the reinforcement of the motor mounts. Maybe keep the following in mind to avoid repeated cracking:

Am assuming that "Far easier that resin..." should be "Far easier than resin..."

Re: how to install the sealant, and which one to use, thanks. Have read this is the proper way to bed a backing plate, but glad to have your confirmation.

Just realized that this means I will need to drill the new backing plates before I install them. That means I will need a second set of hands to mark them from above while I hold them in place, unless I can rig up something to hold them. Hmmm. Now that I think about it, I have a couple of "Little Hand" cabinet installation supports. They might do the trick.

Use a grinder as you're only taking out four (4) 3" wide sections at right angles. Old plate can remain.

Re: using an angle grinder to remove just enough of the existing backing plates + 5200, great idea. One thought: Since the 3" plates will be centered under the holes, probably only need to remove 1-1/2" to 2" sections of the old plates.

Final gel coating can be done down the road.

Literally and figuratively! Will be easier to do this when the boat is back in our yard.

Thanks again, @Ralph Johnstone. Really appreciate your advice!

Rob

 

[Ralph Johnstone]

Just realized that this means I will need to drill the new backing plates before I install them. That means I will need a second set of hands to mark them from above while I hold them in place, unless I can rig up something to hold them. Hmmm. Now that I think about it, I have a couple of "Little Hand" cabinet installation supports. They might do the trick.

Use tape measure and give the holes about 1/8" slop should be close enough. Have you ever used a glue gun for hold things temporarily in place ? As long as the glue dots re small, they break right off.

 

[robm]

Use tape measure and give the holes about 1/8" slop should be close enough. Have you ever used a glue gun for hold things temporarily in place ? As long as the glue dots re small, they break right off.

I'm right now over not thinking of using a glue gun.

Fabulous suggestion. Thanks.

 

[Ralph Johnstone]

Re: how to install the sealant, and which one to use, thanks. Have read this is the proper way to bed a backing plate, but glad to have your confirmation.

Because these surfaces are sooooooooooo big, I say just overapply your sealant and as long as it oozes out everywhere, you know you have 100% contact. The type ? whatever your hand falls on first. And it lasts for the life of the boat.

 

[robm]

Hi all.

Apologies for being a bit out of touch; ended up not being able to do any work over Labor Day weekend.

Status as of yesterday:

• Removed motor and motor mount. This was made much easier by using an outboard motor harness & a Spitzlift receiver mount crane.
• Made a couple of wood mockups to use as templates for the aluminum backing plates.
• Cut and drilled backing plates from 3” x 3/8” aluminum bar stock.
• Dry-fitted the backing plates. One of them fit perfectly, but the other required some minor modifications (made them last night).
• Had to modify the design from what I was originally planning to do based on the excellent advice provided earlier in the thread. I’ll explain in more detail later, but the short version is that I am leaving the existing backing plates in place, and am going to straddle them at 90° with the new backing plates. Will cut a G10 plate to epoxy to the underside of the horizontal transom section to fill the gap between the existing backing plates under the new cross plates.
• It looks like I’m going to have to reinforce the entire interior of the horizontal transom with backing plates. I don’t know what has caused everything to become so flexible, but it looks like the cracks around the rudder mount hump are becoming more visible.

 

[Ralph Johnstone]

It looks like I’m going to have to reinforce the entire interior of the horizontal transom with backing plates. I don’t know what has caused everything to become so flexible, but it looks like the cracks around the rudder mount hump are becoming more visible.

OUCH ! Looks like the bouncing of the engine may have softened the whole structure. When installing the horizontal backing plates, see if you can reinforce them as well by attaching to the vertical walls as much as possible. Bit of a bugger that you'll be working overhead on the attachment process. Maybe flip the boat over ?

 

[Crazy Dave Condon]

Disagree about tying into the vertical walls. Experience tells me not a good idea.

The original backing plates were too narrow and not long enough particularly the one on the port side most forward one. It did not extend long enough as I saw the cracking at the forward edge inside. A large plate preferably stainless steel to fit both screws would be suggested as that is taking the most stress from the motor.

Suggested a quick disconnect for the electrical line to the motor using a two prong trolling motor plug. I would not recommend the quick disconnect at the motor

As for the wheel steering, hunter used Edson as I suspect the lewmar system was aftermarket. I cannot comment on the rudder unless pictures are posted to the actual hookup to the rudder. The 25’s I sold had Edson steering.

 

[robm]

Quick update:

• Minor mods to the new aft cross aluminum backing plate were successful. Both plates now fit properly.
• As noted by more than one person, the underside of the horizontal transom / swim platform is not uniformly flat.
• Am going to cut some temporary pieces of 1/4 sanded exterior plywood to use as templates for what I think will end up being G10 plates bedded with thickened epoxy to fill and level the spaces between and around the factory aluminum backing plates.

That said, what I really want is to find someone to repair it for me. Unfortunately, I have received zero responses to my queries to a few local boatyards. Must be nice to have too much work to return calls or emails.

Will finish the temporary repair tomorrow morning, and see if it reduces the flexing.

Fingers crossed.

 

[Crazy Dave Condon]

@robm

So often I am asked to help and some never respond. If you were close, I would offer my help for a cup of coffee and a handshake.

 

[Ralph Johnstone]

That said, what I really want is to find someone to repair it for me.

Why would you want someone else to do an inferior job to what you can do at a price that will leave you reeling ?

From your discussion here, I would say you are more than able to complete the reinforcement in a professional manner.

 

[robm]

Hi all. Hope your Fall is going well.

Quick update:

• Had to defer the proper repairs until later this year. Too many things do to, and not enough time.
• Cut a piece of 1/4 sanded exterior plywood to use as a temporary spacer between the existing backing plates.
• Installed the plywood spacer and the new aluminum backing plates using longer bolts through the existing backing plates. This stiffened the platform somewhat for the end of season move, but is not a permanent fix.
• Tipped the motor up to 45 degrees, and lashed it to the nearest pushpit support using a ratchet strap with end loops.
• The plywood spacer mentioned above will be used as a template for the G10 plate that will be the proper fix when bedded with thickened epoxy to fill and level the spaces between and around the factory aluminum backing plates

Will update this thread when I have time to do the repair.

Best,

Rob

 

[Ralph Johnstone]

Tipped the motor up to 45 degrees, and lashed it to the nearest pushpit support using a ratchet strap with end loops.

Did you mention it before or have I just forgotten ........... what is the maximum angle the engine can be tipped for trailering ?

 

[Crazy Dave Condon]

The motor should never be tipped when trailering. If it slip could cause damage. If you have to tip up consider alot less

 

[Steve-o5911]

I have the same boat, a Hunter 25 Shoal Draft 2007.
I have none of this, and I have used this boat heavily. Heavily - trailered down to the Keys numerous times, sailed all over Miami and Timbuktu.

I think either :
#1 A car rear ended your trailer / outboard / rudder and you didn't notice.
#2 The outboard or rudder hit something very hard underwater going very fast.

my guess is #1

 

[robm]

Hi all,

Apologies for a very long lag in following up. I will be posting a detailed update about the repair and our experience with the yard that did it.

Rob

 

[Crazy Dave Condon]

@robm

Keep us posted. final two questions
Look at bottom of motor to see if it ever dragged on anything. I am not sure but was anything struck on the back of the motor, rudder and/or transom?

Dave