Jump to content
Robalo Boating Forum

Recommended Posts

Hey guys, 

First off this is my first ever forum post. However I’m renovating my 1999 Robalo 2100 bay hunter and it has turned into a big project.

I’m having trouble finding any type of schematics or diagrams for any part on this hull. Any input regarding the 2100/2109 tunnel hull differences would be greatly appreciated.

Additionally, if anyone knows where I can’t find older robalo manuals, blueprints, schematics, diagrams, specifications, or any type of technical date related to this specific hull would be great. 


-Tony D 







Link to post
Share on other sites

Hi Tony and welcome to the forum.

Unfortunately, we do not have anything on the BayHunter model.  1999 was the time frame Brunswick Marine owned the company , then Chaparral purchased them in 2001.  I don't think you would have any luck contacting Brunswick.  I would start with contacting Chaparral customer service as they may have some some of the documentation you are looking for in their archives.  If they do have anything, please post the documents here so I can add them to our on-line resources.

So what's the story on the boat?  Curious as to why you are removing the cap.  Not many people have gone that far into a Robalo before.  Please take plenty of pictures and keep us posted on your progress.  Also, don't be shy to ask questions.

Link to post
Share on other sites

Thanks for the information, that explains why my hours of searching wahoo, Brunswick, chaparral, and robalo databases has lead to zero information on this bayhunter. I have a robalo and chaparral dealer close to home I’m going swing by and see if the can lead me somewhere this afternoon and I’ll follow up. 

As far as the story goes, I purchased this boat May 2019. Last summer I noticed some floor sag and the T-top was flexing the floor during operation. So I’ve finally got around to this project replace the floor but while doing so I discover a termite infestation in the transom/stringers/floor and basically any part of the boat that has a wooden core. (I parked it along a tree line for about 6 months while waiting to find the time to get around to fixing her) 

So the new plan is replace  the stringers, transom, floor, and all other wood that is on the boat. Basically, I’m going to try building a new boat.. Heres the progress so far and yes you’ll see in the pictures the damage is extensive. 








Link to post
Share on other sites

Looks like a fun project for and adventurous person!

If possible, before you start cutting the stringers out, level the hull the best you can and add blocking at each corner at the transom, blocking half way up the hull on both sides of the keel, and one block forward under the keel.  Use wedges to make sure all point are supporting the hull.  The reason for this is to keep the hull from developing a  hook or rocker once the stingers and cross members are cut out.

Before cutting the stringers out, cut the glass off the top of the stringer and see how hard it would be to remove the rotten wood while retaining the glass on the sides of the stringers.  If the glass is still solid, this will help hold the hull shape.  You will also be retaining the proper height so the cap can be re-installed with ease.  If all looks good, fill the void where the stringers were with foam and trim the top when cured.  Then scuff the sides of the glass stringers and about 8 inches on the hull, then glass 2 or 3 layers of 1708 biax cloth over the stringers and onto the hull to increase the tabbing area.  When finished, you will have a fiberglass composite frame grid with no wood to be concerned with.  After all this is done, install some drain holes to allow any water that  may get trapped outboard of the stringers to drain to the bilge.

Even without schematics, you now have a blank sheet of paper to install new rigging tubes for wiring.  Keep the original tubes going to the transom, but seriously consider adding a second one running back there for any future projects.  Much easier to put an extra one in now instead of wishing you did it a few years down the road.  While you are at it, run one forward for the trolling motor wiring, nav and courtesy lights, and possibly an anchor winch.

Link to post
Share on other sites
  • 4 weeks later...

Somebody has been very busy!  What you have accomplished is fantastic.  I like the stringer grid work, too.

Are you using vynilester or epoxy?  Where the t-top bolts to the floor, what material are you using for the coring?  If you know the approximate locations of the legs, you could fiberglass or epoxy some 3/8" or 1/2" aluminum pads to the backside of the coring material.  Determine where the holes need to be drilled once the cap is back in place, drill pilot holes then tap the aluminum to accept the appropriate stainless steel fastener.  This will minimize the potential for pull-out.  You can also over-drill those holes and epoxy a section of pvc/cpvc tubing to act as bushing and seal the core from water intrusion.

One suggestion if there is room to allow for it.  Where the stringers tie into the transom, is there enough height below deck to allow a knee on the top of each stringer so you have more stringer surface tied into the transom?  My thoughts when I rebuilt mine was anything that could be done to minimize the torsional effect of motor pushing and pulling on the transom (they do exert a lot of force when you pull back fast on the throttle at speed) would not hurt overall performance.

Link to post
Share on other sites
  • 1 month later...

Darn nice job!  You put that thing back together built like a tank...much better than when it left the factory new.  (Granted, they did not have the fancy composites back then to work with.). That boat has its life extended by at least 20 more years.

Was the Arjay used for bedding the cap to the stringers?  And did you use that high dollar spray gun for the entire boat?  I have heard others complain about those guns, but I have used them for a long time with good results.  The HF $15 spray gun can be easily converted to shoot gelcoat; just need a 2.5 air cap and needle.  The bodies are identical to other brand gelcoat guns that cost $75-100, right down to the same casting markings.

Link to post
Share on other sites

So, as the project nears completion I would like to give some technical specs on my repairs and customizations and details on materials used. And the pros and cons of each decision that was made throughout. 

Initially, this was going to be nothing more than a floor repair. Once I dug into the boat a little more I discovered that the entire hull from top to bottom was riddled with termites, and every structural component of the vessel was jeopardized. I then determined that this boat was going to have to face a complete reconstruction including the stringers, transom, and the floor. I began doing my research on stringers and found that new/modern engineering on stringers was a wood-free design that only used a high density foam as a coring material. The transom also followed suit on modern manufacturing techniques with a composite material as a core (coosa) and the floor was reconstructed using coosa as well. 


I decided to throw out the original design/layout of the stringers and built my own “grid” style stringer and cross member system that maximized the structural integrity by adding additional crossmembers and thickening the fiberglass composing them. This allowed the floor to have more surface area for support  while simultaneously adding a significant amount of hull strength. The high density foam core is encased with a single layer of 1.5 oz chopped strand mat followed by 3 additional layers of 1708 bi-axial cloth (4 layers in most of the corners just to be extra cautious because I’m not a structural engineer). The aft hatch floors and central gas tank support are PVC board encapsulated in 1708 bi-axial cloth and tabbed into the stringers/transom by another two layers of 1708. I wanted completely encapsulate the PVC board because I wasn’t sure how good the bond would be between the polyester resin used with my fiberglass would be to a pvc surface. 


With the transom I was able to remove the original rotten “‘marine grade” ply and salvage the outer hull. This was convenient for multiple reasons because all the original holes for drains, trim tabs, motor bracket etc. would all be there and I could just drill them out once I had my new transom complete. The coring material for the transom is coosa board sandwiched together with multiple layers of 1708 between. Basically the transom is comprised of this starting from outside in (Hull, 1708x2, 1/2in coosa, 1708x2, 1/2in coosa, 1708x5) it’s EXTREMELY strong.. each of the 5 final interior layers of 1708 is tabbed in 2 inches further to the hull on each overlay. 


once again I managed to salvage the original floor layer that is in the cap/insert mold and I used coosa a coring material for this as well.  It is original floor glass, 1708x2, 1/2in coosa, 1708x2. Once again very rigid and excellent structure from the coosa.  However the coosa is not a good material to secure into because it doesn’t thread well because of its composite properties. So where the t-top and leaning post were going to be secured I placed a 1/2in sheet of aluminum as a backer plate and secured it in place with epoxy  (and then put a layer of 1708 over all of these so they didn’t fall off while I was drilling pilot holes once I got everything back together because at that point they would be inaccessible) 



Link to post
Share on other sites

Once all of the structural repairs were completed I then began the reassembly process where I had to place the cap back onto the hull. For this step i used the same process as most modern custom boat builders and used Arjay 4100 core bonding compound. This is an extremely strong and reliable (and expensive) polyester based putty that has high PSI tolerances and the ability to flex while maintaining its bonding integrity. While constructing the new stringer system I left approximately 1/2”-1“ gaps between the floor and the top of the stringers to leave room for this bonding compound. Just before lowering the cap back down I mixed 4 gallons of Arjay 4100 (mekp catalyst) and placed a huge bead approximately 2 inches tall all over the stringers. The arjay only has about 30-40 minutes of working time once mixed up so I wasn’t able to get pictures of this step. Then lowered the cap back down into place the put a little pressure on it with straps and floor jacks and let it cure in place overnight. It somehow worked out flawlessly. This was a crucial step that HAD to be correct the first time. Fortunately it worked out flawlessly and everything was straight level and STRONG. 

Link to post
Share on other sites

Thanks for the added details.  You did everything that is found in most boats today.  The aluminum backer blocks was a very good addition and the explanation for doing it is dead-on.

The only "mistake" I see is the same darn thing I did when re-doing my boat...too many layers of 1708!  I was a firm believer of trying to match the original fiberglass thickness used back in the '80s when they used roven woving and chopper guns.  The problem is the 1708 biaxial fabric is so much better since it is engineered with the oriented fibers for optimal strength, we really did not need all those layers!  I was proudly telling the owner of the fiberglass supply house how many layers of biax I used on the transom and he chuckled then said he did not realize I was building a tank!  3-4 layers would have been sufficient and still yielded a stronger laminate than the original factory job.

But...the way you extended your tabbing onto the hull in 2 inch increments really spreads the load over a wider area along the hull and makes the back end rock solid.  And I am glad to see those pictures of the grid system below deck.  There is no comparison to what was originally in there.  Not only is the hull stiffer now, I bet it is not nearly as noisy as before, too. Plus the added strength supporting the deck.  I did not realize the Arjay had that short a working time...you guys must have been scrambling during that short work window.

Link to post
Share on other sites
  • 6 months later...
  • 2 weeks later...

What you did to that boat is fantastic!  If it was not for the pictures of the rebuild, I would have thought it was a new hull...especially how the bay boats are so popular now.

I am curious if you noticed any change in how it rides now?

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...