Solid keel for SIB?

[benton0311]

Does anyone have any experience with running a solid keel in a SIB, like what Bombard does on their boats? How do they compare to inflatable keels? I'm mostly concerned with how well the keel cuts through waves.

I trailer my current 15-foot SIB and I've already installed stainless tubes to reinforce the floor panels which made the boat feel more solid and handle slightly better. I do run the correct pressures but still wish it cut through waves better and I'm wondering if a solid keel would provide an improvement compared to the inflatable keel compressing slightly on wave contact.

I've got one of the new Saturn 18ft SIBS coming next month and, since I'll have everything apart and will be doing some light fabrication, then would be the time to tackle my keel project if it's feasible.

Not sure how I would make it, but probably either wood 2x4s or TREX boards that have been glued & bolted together and profiled for the contour of the hull. I'd then bolt the top to the aluminum floor which is then longitudinally reinforced with stainless tubes.

 

[Sea Rider]

If you want a solid keel, remove the upper air valve with an extractor tool,



once out remove the middle spring and pin unscrewing the small black/grey screw located right in middle of the vertical pin, when done screw the upper air valve back in tight onto the lower valve and fill the inflatable keel with rubber foam or any other material that will harden over time to form a solid shaped keel. Take advantage that's it's already glued there, why mess with it.

What gives hull fabric rigidity it's a combo of well inflated side tubes to their recommended working pressure say 3.5 PSI, 0.25 BAR or higher, that's with a pressure gauge along...



max keel pressure allowed to form a solid hull V tent under the extension of the alum floors to cut water more efficiently, not as neat as a Rib though. It's a very bad idea to mess hard against tall waves, swells rough sea conditions at speed, will end screwing (bending) both Z rails that holds the alum floorboard panels together and fits into the large side stringers specially on large Sibs. If in need to pass waves, swells negotiate passing them sideways at reduced speed, you back and but will thank you...




What do you plan doing with a 18 footer Sib powered with which HP and brand motor ?

Happy Boating​

 

[benton0311]

I'm definitely tracking on the importance of tube pressure and always inflate to 3.5 psi mains and 4.5 psi keel (supposedly the keel should be at slightly higher than the sponsons). However, on my present SIB, I modified the floor so it's bolted to stainless steel tubes on both sides so it's solid as a rock. I plan on doing the same with the new boat as well.

I almost always take tallish waves at an angle and a low-to-moderate speed. The issue isn't so much the tall waves but the choppy waves - short choppy waves can be brutal sometimes. Actually tall waves with a low frequency are really easy to manage, it's the frequent little choppy ones I'd like to cut through better. The ocean usually isn't too bad but some of shallower bay areas I frequent get churned up pretty easily in any kind of wind. Not big waves, just a lot of chop. I'm not sure if a solid keel would make a difference, but I've been fascinated by Bombard's approach to the solid keel and wondered if maybe it would help cut through some of the smaller waves.

The 18 ft SIB will be used in a mix of bays and ocean along with inland lakes and reservoirs. I'll be using my present motors on the 18 footer - a 40 hp 2-stroke Yamaha-Mariner for bays/ocean and a 110 lb Haswing brushless trolling motor for electric-only lakes. I'll be hauling my family of five+dog for fishing, swimming, and general exploring of different coastal waterways which is what we currently do with our existing boat.

Your idea to fill the keel tube with a solid substance is very interesting, I may need to investigate that option further. That would certainly be a lot easier than cutting out the existing tube and fabricating a new beam for the keel.

 

[Sea Rider]

How many side joiners pieces does the 18 footer sib have per side, the one that locks the Z rails in place ? Can you post some pics of the modified bolted floors to stainless steel tubes to have a look ?

Adding a hardened keel to a Sib won't better much the handling on choppy windy water conditions as the Sib will be jumping over them and smashing the hull against the chop depending on speed creating unwanted unconfortable rides for passengers specially the ones seated at bow and middle Sib.

Been sibbing for years and when decided it was time to pass to Ribs with hard deep V hulls thinking that those inflatables would cancel jumpy unconfortable slamming rides on choppy windy waters I was wrong. The hard solid hull riding way higher than the water level will bang much worse than a Sib which will accommodate itself much better on the water level.

An air keel although it's inflated to a much higher pressure than side tubes has so small air volume that tends to deflate itself due to working on top of the hull fabric which rests very close to the water level which can change due to atmospheric conditions, water temperature that will deflate the keel.

If counting with a solid keel as the Bombard Sib will forget all about reinflating the keel again and as long the side tube are working with their recommended pressure the tent formed under the hull will remain well stretched and provide a better water ride. Those keels are articulated, it's not a one piece long keel.

Happy Boating​

 

[benton0311]

How many side joiners pieces does the 18 footer sib have per side, the one that locks the Z rails in place ? Can you post some pics of the modified bolted floors to stainless steel tubes to have a look ?
​

I'm looking at the photos of the 18 foot Saturn on the website and it looks like it only has two joiners per side. My current 15.4 ft boat has 3 joiners per side. I'm not sure how accurate the photos on the website are though, since the Saturn I ordered is a newer model with some hull improvements and other changes while many of the photos on the website are of the older model.

Below are some quick photos of the floor and port side stainless tube. Sorry the photos aren't the greatest, it was getting late and I still had the cover on the boat. It's a 1" square stainless steel tube with .065" wall thickness. It runs the entire length of the aluminum floor all the way back to the transom, with three bolts attaching it to each panel. I plan on doing something similar to this on the 18 foot boat.





Since I trailer the boat, I love how the stainless tubes reinforce the floor and make it feel even more solid - it doesn't give at all. They're also nice because they make good attachment points for tie downs and swim ladders, and I could even brace the transom to the floor tubes if I was so inclined. It might be a placebo but, even with correct pressures, the solid floor makes the boat feel very slightly more solid and responsive in the water, like it has a solid reinforcement structure running through the center. It also helps the ride on the few occasions I've let pressures run low - the boat still handles poorly when underinflated but it still has some center stiffness to help out.