Can I safely transport a 18.5 Oscada fiberglass canoe weighing 75lbs. on roof bars that are 4 Ft. apart without front and end bracing? This will be just to get it home 300 miles. I don't know how much stress this would put on the bow and stern. Canoe will be upside down. I have eye on a used Oscada but I don't know what model is is yet.
We used to carry an 85 #, 18.5’ canoe
on a Renault 16 with even smaller crossbar spacing. But you need to improvise front and rear tie downs, preferably triangulated, that is, ropes going outward from each end of the canoe to some tie point on the bumper. It is also possible to mount tie down loops in the cracks surrounding the hood and the trunk lid, but that can come later.
I have driven thousands of miles with an 18’6" canoe on top with less bar spread about the same. YOu should triangulate the bow so cross drafts don’t shift it. (bow tie downs) and I would suggest a stern tie down also in this case. use good straps for the belly bands, or learn the truckers cinch.
Yes…18’ wood/canvas on orig VW Bug
Back in the day...granddad's 18 footer(wood/canvas) went on his 66' VW Beetle. Was a little interesting in a wind, on the highway...but back then noone had to go over 50.
Think if you tie the ends to each corner of vehicle and tie each thwart to one or maybe both rails it'll be solid enough for anything.
Do what everyone is saying, and provide dual tie-downs at each end of the boat to help keep the ends from shifting back and forth. However, it is quite likely that you can get even better side-to-side bracing, especially at the back end of the boat (which is likely to overhang well beyond your tie-down points on the car) if you provide such tie-downs a few feet AWAY from the ends of the boat as well. Attach these ropes to thwarts or seats. These will be shorter ropes, providing their side-to-side bracing in a much more efficient and "direct" manner (the direction of bracing will be more closely aligned with the orientation of the ropes the ropes don't need to be nearly as tight to get the same effect as they'd need to be otherwise, which illustrates how well this works). If nothing else, doing this in addition to tying the ends will greatly increase the boat's resistance to being shifted back and forth. I've done this with a minimum number of ropes (two at each end) as well as with three times that number, and increasing the number of ropes and attachment points, as well as tying them at more-efficient locations than the very rear end of the boat behind the car, truly makes a huge difference.
Why not use front&rear tie-downs?
Are you asking because you can’t find easy spots for the front and rear tie-downs? Easily solved for the front - put rope or cloth loops under the bumpers for the hood, should be one at each front corner and run a line between them. And make sure it is knotted so that the bow can’t slide side to side, that the middle point is fixed. The rear probably has something along the bottom frame if you look. And use two straps rather than one at each point where it is strapped to the racks - or two ropes if ropes.
I would suggest that you make sure the driver can still see though - the arc of that canoe could be deep enough that a tall person could be challenged seeing ahead. If I am not attentive the direction I put the Merlin up in, even I can feel like I am seeing under a tunnel.
a suggestion …
........ add one or two straps snugly around the "canoe only" inbetween the 4' bars to help counter the effects the bending moment will have on the canoe's midsection with such a two ended cantilever (I'm assuming you intend to maintain an equal cantilever , same amount of overhang both front and rear) .
To give an example of a bending moment effect dramatized ... picture the canoe ballanced on a single cross beam ... apply pressure downward on each end ... the center section of the canoe wants to take on a different shape (deform) , most likely expand . Although you have two beams at 4' apart the bending moment effect is reduced "some", not cancled by any means . And more so the 7'+ cantilever from each end will increase (magnify) the effects of stress through the mid-section greatly on each bounce and bump the auto takes . A couple extra straps around the canoe only (perhaps just ahead and behind the center yoke/thwart) to help brace the center section against this amplified stress during bounce and bumps should be very helpful I think . Cantilevers magnify forces greatly , think about the power of a lever .
That’s why nobody makes their tie-downs
... really tight - at the boat ends that is. Those tie-downs will get more snug if the boat shifts position, always exactly counteracting the force applied by the boat as it tries to move, but when the boat's not being pushed one way or the other, the end tie-downs aren't really pulling very hard at all. In any case, what you describe is an attempt to counteract 7-foot lever arms with 2-foot lever arms, and since the applied force in the same location for both 2-foot lever arms, you are needing a big force. Just from the standpoint of levers, that's analogous to trying to ride a road bike up a steep hill in high gear. Besides, since the car is a lot wider than the canoe, to apply that much force in the downward direction you'd need enormous tension in that center strap or rope (of course you could drill holes in the roof to allow that center strap to pull straight down, eliminating the need to use 50 or 100 times as much tension as the desired tie-down force). If a boat really WERE fragile enough for this to be a concern, applying a big load to the boat's center would only add to your worries. You'll notice that people with fragile racing boats sometimes use alternate strategies (such as extra-long roof-rack frames to eliminate the need for super-tight sideways restraint).
Don't over-think it. The canoe won't be damaged. With "barely snug" tie-downs at or toward each end, if you do a good job of orienting the tie-downs to match the desired direction of force the boat will only shift a little, and if you do a bad job it will shift more, but either way, it won't be going anywhere.
gbg , what you describe is …
...... as a diving board platform . Not even trying to go there . Just suggesting a little extra circumfrence bracing (with straps) in the mid-section (think girdle or elastic body brace) . Don't underthink it , the mid-section has to endure a 3.5 to 1 amplification of the bending moment forces . Whatever the 7'+ cantilever weighs , that will be magnified proportionally to stress the center section when the ends dip downward during bump and bounce of auto . Simply adding a couple extra straps snuged up around the canoe only can't hurt anything ... but from your response I gather you feel it can't help anything either .
End tie downs as you described are basically shock cords not meant to be torqued to tight (especially with greater cantilevers) , that I completely agree with . They aid in arresting lateral and upward movements , as well as rearward or frontward movements , are also good idea for countering catostophic failures ... they haven't any ability to prevent bending moment stresses through the center section ... I think a couple straps could be helpful here as "reinforcement" to the center section , that's all .
Small investment for a couple extra cam buckle straps (that could be used elsewhere on other occasions) , 1/2 minute to apply them ... but if they are useless in the way I have suggested , then my suggestion is useless ... but I don't think so .
Anyway , how's it going ... you ready to ring in a new year , ready or not here it comes ... happy new years to you and all !!
Use poly straps,
which are more secure than rope.
I used to tote an 18.5 Sawyer Super on top of a Porsche 911. Worked fine!
The trick is to use 4 separate ropes, two at bow, twp at stern to the four corners of the car to control the stems.
That’s different than what I thought…
… you meant. I actually don’t think bouncing force on the ends is any big deal, since is dampened by the car’s suspension so much. I’ve never seen any evidence that it happens.
However, the straps you describe are a good idea just for making the boat more secure. For what it’s worth, I do exactly what you describe, but with the ropes positioned to work a bit more efficiently. Since I have a longitudinal bar on each side, far out beyond where the canoe sis, I can put one two loops at each cross bar, and for each pair of those loops, one snugs the canoe to the right, and the other snugs it to the left. They take the place of gunwale blocks, and IF wrapping the canoe to brace against the forces you describe is needed, these four ropes would work more efficiently for that as well (and would do so with much less overall tension because the anchor points are located closer to the best direction of pull). This actually works pretty slick for really solidifying the boat to the rack, and it could also be done, though needing quite a bit more rope tension to get the same effect, by tying off to the cross-bar towers.
As far as the New Year goes, it is traditional to paddle on a huge power-plant cooling pond near here on Hew Year’s Day, but that really has little appeal for me, and having lunch in the bar afterward is the better part of the event. I might skip it this year and go hiking instead.
Again, watch that overhang
If the canoe overhangs the end of the car, as almost certainly will be the case at the rear, ropes going all the way to the stem are terribly ineffective at controlling side-to-side motion compared to ropes that simply attach to the canoe at a point nearest the rear corners of the car. The best side-to-side control is achieved by ropes that attach to the outermost corners of the car, but slant neither forward nor backward as viewed from the side. I've posted about this topic on several of the recent car-topping threads - the more the rope deviates from the angle at which you wish to apply force, the greater the amount the boat can shift around due to even very tiny amounts of stretch in the rope. As I mentioned above, the boat won't "go anywhere" with inefficient rope placement, but it's just so much nicer when you can actually limit movement more effectively with a whole lot less rope tension.
mickjetblue, for every person I know who
has had a rope slip loose or break, I know a person whose strap cam slipped or whose strap slipped out of position. For tying canoes, there is no consensus about ropes and straps. Careful use of either will yield good results.
Ropes should be polyester, which does not stretch much when wet, and which stands up well to UV. But I never had trouble with Nylon ropes.
Ropes vs Straps
Straps are more secure for people who don't know how to tie knots, and since that's most people, perhaps it's good advice. Otherwise, I'd say there's no difference at all between straps and ropes, except that securing your canoe with ropes is faster and easier (again, if you are handy with knots).
By the way, a friend of mine gave me a pair of Thule straps, which I use from time to time. I find that one of those straps slips a bit and gets loose on every single trip. I think that will stop happening once the straps get a bit of wear. On the other hand, in 35 years of tying boats on top of cars with rope, I have yet to have a rope get looser. Ropes are totally reliable, no question about it.
can be linked to knot effectiveness and holding power.
Here are some good knots:
I actually use a combination of straps and rope, with the straps used for triangular bow and aft tiedowns, and rope across the middle of the canoe to the roof racks. Using straps from NRS and Strapworks, I have not had any ever come loose. Rope and knots are another issue, as I have had a seemingly good knot work a little loose from storm weather conditions.
I have read somewhere about ropes being illegal in some areas, but I have nothing to back that up with.