Bottom height above the ground when on a trailer?

[DayTripper]

I'm going to start looking for a used trailer for the flat bottom jon boat that I'm building. When a boat is sitting on its trailer, what is the typical height that the bottom is above the ground for easy launching off a boat ramp?

[Peerie Maa]

As low as your suspension will allow. My boat has a 6 inch salient keel, so i built a double spine trailer with the keel rollers slung under the spine to get the boat as low as possible.
Because you have a flat bottomed John boat, I woyld go for a flat bed, with guide rollers to ensure that it is centred.
I fitted guide rollers to ensure that the keel landed in the correct place.
Guide roller.jpg
You will need to install yours at the maximum beam of the bottom. Rollers across the back of the flatbed will be helpfull in getting the boat on and off, for when you cannot float it on.

[timo4352]

The steepness of ramps varies....
For reference my Ninigret sits 26 inches above the pavement at the ass end.
More importantly the skeg of the outboard is about 11 inches aboveground in the down position.
I am able to cross the curb of my driveway with no worries.

[DayTripper]

As low as your suspension will allow. My boat has a 6 inch salient keel, so i built a double spine trailer with the keel rollers slung under the spine to get the boat as low as possible.
Because you have a flat bottomed John boat, I woyld go for a flat bed, with guide rollers to ensure that it is centred.
I fitted guide rollers to ensure that the keel landed in the correct place.
* pic omitted to save bandwidth *
You will need to install yours at the maximum beam of the bottom. Rollers across the back of the flatbed will be helpfull in getting the boat on and off, for when you cannot float it on.

If I can find a small used trailer, I suspect it will come with bunks but no rollers.

My primary concern is what is the typical height of the boat's bottom off the ground. Reason is if the flat bottom has to go "above" the fenders, then how high is sensible to launch off a boat ramp. Thanks for the help.

[DayTripper]

The steepness of ramps varies....
For reference my Ninigret sits 26 inches above the pavement at the ass end.
More importantly the skeg of the outboard is about 11 inches aboveground in the down position.
I am able to cross the curb of my driveway with no worries.

It's very helpful info that the bottom of your transom is 26 inches above the ground. That is the kind of info I'm looking for.
Regarding the skeg of the outboard being 11 inches above ground in the down position during transport, I assume that's because it eliminates the need for a transom saver.
Thanks for the help.

[timo4352]

The bottom can fit "between" the fenders easily....just need to get the right trailer.

[timo4352]

The bottom can fit "between" the fenders easily....just need to get the right trailer.

[Todd Bradshaw]

A 12"trailer tire has an outside diameter in the 21" range. Looking at mine from the stern it looks like the lowest point on the hull might be a couple of inches below the top of the tires. It seems to yield decent ground clearance and I haven't had any trouble launching from ramps or our beach.

w3.jpg
1975 Boston Whaler Sport13

w2.jpg

[Breakaway]

The steepness of ramps varies....

As does the water level in tidal areas.

Lower is better, especially if you have bunks. At low tide, rollers make it possible to unload the boat whereas bunks might see you waiting for the water to rise.
Of course, we're talking a jon boat here, so there will be some ability to muscle the boat on and off.

Kevin

[Woxbox]

I now replace bunk carpet with the slippery plastic covers. It makes getting the boat on and off much easier. As to height, the lower the better.

[Canoeyawl]

The lower the better, both my larger boats are about 6"-8" keel to ground right aft. The keel is at zero clearance from the top of axle if the axle bottoms on the suspension.

[DayTripper]

Breakaway said:
Lower is better, especially if you have bunks.

Woxbox said:
As to height, the lower the better.

Lower would definitely better for launching.

But what is the typical height in inches, that the bottom of the transom is above the ground when on a trailer? Not specifically for a jon boat but the usual 17 to 18 feet boat. Then if folks can launch their boats at that height, I will be able to launch my jon boat too without muscling my boat off/on.

Need the height info so I can determine if a used trailer can be adapted to have my jon boat fit on it with acceptable transom height above the ground.

Thanks.

[stromborg]

I don't think that you are going to find "typical". Too much variation to account for between wheel sizes and types of axles not to mention the actual bed construction. What are the other jon boaters out there using? How deep are you willing to drive the trailer?

ETA:
Google showed me this: a 1250 gvrw jon boat trailer with a ground to bunk height of 22" being from Karavan, I'm guessing that is reasonable number.
https://www.karavantrailers.com/prod...specifications

[DayTripper]

I don't think that you are going to find "typical". Too much variation to account for between wheel sizes and types of axles not to mention the actual bed construction. What are the other jon boaters out there using? How deep are you willing to drive the trailer?

I haven't seen any jon boats which is why I'm building mine.
Regarding how deep am I willing to drive the trailer, I don't want our van's tires to go over slippery moss and have our van slide into the water and become immersed. I think I need to visit a launching ramp at low tide in the morning and watch the boats being launched. Observe whether the vehicle's tires contact moss on the ramp. Might have to figure out a tongue extension for which ever trailer I'm able to find.

ETA:
Google showed me this: a 1250 gvrw jon boat trailer with a ground to bunk height of 22" being from Karavan, I'm guessing that is reasonable number.
https://www.karavantrailers.com/prod...specifications

You have superior Google search skills, much better than mine. I've been Googling for hours and never found even one website with the dimensions like the Karavan 1250 trailer you linked to. That trailer would be the "perfect" trailer for my jon boat. A search for Karavan dealers shows Home Depot but I never saw a boat trailer at a Home Depot store in our area. I'll ask customer service the next time we visit Home Depot.

Thanks!

[Breakaway]

I haven't seen any jon boats which is why I'm building mine.
Regarding how deep am I willing to drive the trailer, I don't want our van's tires to go over slippery moss and have our van slide into the water and become immersed. I think I need to visit a launching ramp at low tide in the morning and watch the boats being launched. Observe whether the vehicle's tires contact moss on the ramp. Might have to figure out a tongue extension for which ever trailer I'm able to find

Your tires will certainly be on slime and moss when launching on a falling tide. Its a good idea to carry and use wheel chocks. While sliding into the water is good to be aware of, a jon boat isn't likely
heavy enough to pull your vehicle in. Also, many ramps are textured or siped to provide traction. Again, it depends.



B

ut what is the typical height in inches, that the bottom of the transom is above the ground when on a trailer? Not specifically for a jon boat but the usual 17 to 18 feet boat. Then if folks can launch their boats at that height, I will be able to launch my jon boat too without muscling my boat off/on.

A Vee hull on rollers will be closer to the ground than a similar size flat bottom boat on on a similar size/ wheels bunk trailer. Again, it depends.

If pressed, I might say eight inches minimum. But you may have a bumpy, rutted driveway, or road to the ramp, which would probably see me wanting more clearance.

K

Kevin

[DayTripper]

Your tires will certainly be on slime and moss when launching on a falling tide. Its a good idea to carry and use wheel chocks. While sliding into the water is good to be aware of, a jon boat isn't likely
heavy enough to pull your vehicle in. Also, many ramps are textured or siped to provide traction. Again, it depends.

I'm thinking that just the weight of the vehicle can be enough to have it slide into the water since the boat (any boat) will already be floating at that point. The trailer will be fully submerged so its weight will be less in the water plus the buoyancy from the air in the trailer's tires.

A Vee hull on rollers will be closer to the ground than a similar size flat bottom boat on on a similar size/ wheels bunk trailer. Again, it depends.

If pressed, I might say eight inches minimum. But you may have a bumpy, rutted driveway, or road to the ramp, which would probably see me wanting more clearance.

Kevin

My concern is that since the bottom of my jon boat is 46" wide, it may have to be above the fenders on a small trailer. If the small trailer has small diameter tires, then maybe the bottom of my boat can still be 22 - 24 inches above the ground. Looking for a used trailer, having the boat fit between the fenders may not be an option. Just gathering info to have on hand when evaluating a used trailer.

Thanks.

[Breakaway]

Perhaps spend an hour at high tide, and then at low tide, observing boaters using your local ramp. I think that will give you a feel for things.

Kevin


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[DayTripper]

Perhaps spend an hour at high tide, and then at low tide, observing boaters using your local ramp. I think that will give you a feel for things.
Kevin

Thanks Kevin. I will do that.

Last night I made a drawing using Sketchup. A trailer with 3 feet of tongue extending beyond the bow of a 12 foot flat bottom jon boat. With the trailer on level ground, the bottom of the transom being 24" above the ground. A boat ramp with a 10 degree slope.

At high tide with the ball of the trailer right above where the water level meets the ramp, there will be 7 inches of water depth at the bottom of the transom. Probably enough to float a flat bottom jon boat off the trailer. All 4 wheels of the tow vehicle will be on dry, non slippery ramp.

Problem is if water level at low tide is 2 feet lower than high tide, the wheels of the vehicle will be on the ramp which may be slippery from moss/algae. Still need to work out whether the front wheels of the tow vehicle will be on dry moss/algae free ground.

Any how, it appears that if the bottom of the transom is more than 24" above the ground when the trailer is level, a tongue extension is needed to float a 12 foot boat off the trailer with the tow vehicle's 4 wheels on dry, moss/algae free ground. The longer the boat, the less this is a problem. IOW, the longer the boat, the better the float.

Still working the scenarios out.

I will take time at a ramp to observe boat launchings. Especially at low tide. Thanks.

[hawkeye54]

Day Tripper, I wrote a response to this thread which got ' lost' - to summarize, can you fit a hitch receiver to the front of the van, and push the boat and trailer down the ramp while keeping the rear wheels safely on dry paving surface - then back the rig out to pull the boat / trailer up the ramp ?



Rick

[Woxbox]

I've been launching boats for over 40 years, and it's my experience that going to great lengths to float the boat on and off the trailer isn't worth the trouble. Whether it was my 27' trimaran or my 16' plywood skiff, or anything in between, I've always found the easiest method is to back down until the transom starts to lift, then stop the vehicle, free the boat and shove it off the trailer.

If you do this, the rear wheels of the tow vehicle will not have to be in the water. And if the boat is on bunks but the bow is on a roller, once the boat starts to float, the boat will slide off pretty easily because it's not bearing on the bunks anymore.

Retrieving the boat is the opposite. The trailer is in deep enough that the boat can be run onto it with the bow coming to a stop 2 or 3 feet maximum from the winch. Hook it on and crank it up the rest of the way. If your trailer is well set up, the boat will self-align as you crank it up. If you try to float it all the way on, it's much harder to keep the boat lined up on the bunks when you load it and drive it up the ramp.

To make this work, it can take some fiddling with the roller positioning under the bow. Usually you'll need two, and one of the two might not even be engaged once the boat is out of the water. It all depends on the shape of the hull and other geometry.

Also, you want something to center the boat left and right. For a flat-bottomed boat, side bunks are the key. And as I mentioned earlier, hard plastic covers on the bunks are better than carpet.

Here's my current boat on its trailer. Launching and retrieving is a piece of cake. Note the position of the side bunks. They seem high here, but when the trailer is on the ramp and the boat is on its waterline, those side bunks are just high enough to catch the boat and center it. As soon as I winch it up, still in the water, the bow lifts, the stern drops, and it's mostly but not completely settled down on the bunks.

42 road test.jpg

[DayTripper]

Day Tripper, I wrote a response to this thread which got ' lost' - to summarize, can you fit a hitch receiver to the front of the van, and push the boat and trailer down the ramp while keeping the rear wheels safely on dry paving surface - then back the rig out to pull the boat / trailer up the ramp ?
Rick

Our Odyssey is front wheel drive so it will be better to have the trailer hitched to the receiver on the back. Thanks.

[DayTripper]

I've been launching boats for over 40 years, and it's my experience that going to great lengths to float the boat on and off the trailer isn't worth the trouble. Whether it was my 27' trimaran or my 16' plywood skiff, or anything in between, I've always found the easiest method is to back down until the transom starts to lift, then stop the vehicle, free the boat and shove it off the trailer.

If you do this, the rear wheels of the tow vehicle will not have to be in the water. And if the boat is on bunks but the bow is on a roller, once the boat starts to float, the boat will slide off pretty easily because it's not bearing on the bunks anymore.

Retrieving the boat is the opposite. The trailer is in deep enough that the boat can be run onto it with the bow coming to a stop 2 or 3 feet maximum from the winch. Hook it on and crank it up the rest of the way. If your trailer is well set up, the boat will self-align as you crank it up. If you try to float it all the way on, it's much harder to keep the boat lined up on the bunks when you load it and drive it up the ramp.

To make this work, it can take some fiddling with the roller positioning under the bow. Usually you'll need two, and one of the two might not even be engaged once the boat is out of the water. It all depends on the shape of the hull and other geometry.

Also, you want something to center the boat left and right. For a flat-bottomed boat, side bunks are the key. And as I mentioned earlier, hard plastic covers on the bunks are better than carpet.

Here's my current boat on its trailer. Launching and retrieving is a piece of cake. Note the position of the side bunks. They seem high here, but when the trailer is on the ramp and the boat is on its waterline, those side bunks are just high enough to catch the boat and center it. As soon as I winch it up, still in the water, the bow lifts, the stern drops, and it's mostly but not completely settled down on the bunks.

42 road test.jpg

That is quite a boat in the picture. Your van looks small in comparison. The stern of the boat looks to be quite high above the ground, like about 3.5 or 4 feet above the ground. I'm surprised that the stern starts floating with with the rear wheels not in the water. Are the front wheels always on moss/algae free ramp surface? Fresh water so no low tide to contend with?

The side bunks are new to me. Very good idea to keep the boat centered between the fenders. I'll use that idea.

Thanks.

[DayTripper]

Also, you want something to center the boat left and right. For a flat-bottomed boat, side bunks are the key. And as I mentioned earlier, hard plastic covers on the bunks are better than carpet.

BTW, what are the hard plastic covers made out of? Any links to samples? Thanks.

[rgthom]

How much will this jon boat weigh? I assume with a motor it will be too heavy for this, but for a 300 lb skiff with flat sole I found that lead on rollers let me launch with all car tires dry and trailer bearings out of the water. There are bunks to support the boat when loaded, but the rollers and a winch slide it on and off pretty easily on shallow and steep ramps, or even just at water's edge without a ramp.

[timo4352]

Towing with a front wheel drive Odyssey, you're worrying needlessly about spinning tires on the ramp...especially with a lightweight johnboat in tow.

[Woxbox]

That is quite a boat in the picture. Your van looks small in comparison. The stern of the boat looks to be quite high above the ground, like about 3.5 or 4 feet above the ground. I'm surprised that the stern starts floating with with the rear wheels not in the water. Are the front wheels always on moss/algae free ramp surface? Fresh water so no low tide to contend with?

The side bunks are new to me. Very good idea to keep the boat centered between the fenders. I'll use that idea.

Thanks.

The camera lens distorts that view. On level ground, the end of the skeg is just 24" over the pavement. The waterline at the axle is 28" off the ground. Even on shallow ramps, the boat starts to lift off the trailer before the back wheels of the car are in the water. I deliberately set up the trailer so the bow is a bit lower than the stern. When you launch and retrieve, it's the bow height over the road that determines how easy the boat will come on and off -- the back end of the trailer is clearly sunk well down, which is why concern about how high the transom is over the road is beside the point.

A lot of outfits sell the slippery bunk covers. Here's one source from Eastern Marine. They come in different widths and lengths.

[DayTripper]

How much will this jon boat weigh?

So far, without fiberglassing the outside of the hull and painting the entire boat, the boat weighs about 180 lbs (bare without the motor mounted). When the boat is completed, I'm estimating that the weight will be about 200 lbs. The 6HP outboard weighs 55 lbs per the specs. So with the motor and gear aboard, a guess of the total weight might be about 300 lbs.

I assume with a motor it will be too heavy for this, but for a 300 lb skiff with flat sole I found that lead on rollers let me launch with all car tires dry and trailer bearings out of the water. There are bunks to support the boat when loaded, but the rollers and a winch slide it on and off pretty easily on shallow and steep ramps, or even just at water's edge without a ramp.

Are you launching in a lake where 2 feet tidal range is not a problem?
If so, then I see why your tow vehicle's tires will not be on slippery moss/algae.

I've read that the average tidal range in Hawaii is about 2 feet with extreme tidal range at about 3.1 feet.

[DayTripper]

The camera lens distorts that view. On level ground, the end of the skeg is just 24" over the pavement. The waterline at the axle is 28" off the ground. Even on shallow ramps, the boat starts to lift off the trailer before the back wheels of the car are in the water. I deliberately set up the trailer so the bow is a bit lower than the stern. When you launch and retrieve, it's the bow height over the road that determines how easy the boat will come on and off -- the back end of the trailer is clearly sunk well down, which is why concern about how high the transom is over the road is beside the point.

A lot of outfits sell the slippery bunk covers. Here's one source from Eastern Marine. They come in different widths and lengths.

Thanks for the additional info on your boat's setup and for the slippery bunk covers link.

[rgthom]

Are you launching in a lake where 2 feet tidal range is not a problem?
If so, then I see why your tow vehicle's tires will not be on slippery moss/algae.

I've read that the average tidal range in Hawaii is about 2 feet with extreme tidal range at about 3.1 feet.

I was just saying that the ability to launch from above the waterline can be an advantage in many situations, but I expect you are worrying too much. At this tidal slough with my local rowing club we all managed to launch and retrieve in the mud, but my boots stayed a little cleaner since I did not have to go so far down the ramp .

[DayTripper]

Towing with a front wheel drive Odyssey, you're worrying needlessly about spinning tires on the ramp...especially with a lightweight johnboat in tow.

I've seen several youtube videos where the tow vehicles are submerged in the water. We can't afford to lose our Odyssey by having it submerged in salt water.

I'm not concerned about the lightweight jon boat and trailer pulling our van into the water. The boat will be floating before then and the trailer will be lightweight. I'm concerned that the weight of the van on slippery moss/alge at low tide even without a trailer attached might be allow the van to slide into the water. Once the van starts floating, it's all over.

Boats 17 feet long will have a 5 feet advantage over my 12 foot jon boat. Their transom will be in the water 5 feet further in. So I will have to take that into consideration when I go to the boat ramp to observe launching and retrieving at low tide.

Thanks.

[timo4352]

Extend the lounge of the trailer if it worries you.

[DayTripper]

Extend the lounge of the trailer if it worries you.

Yes, extending the tongue is one of the options I'm investigating.
Also, if a trailer is narrow and my 46" wide (bottom) jon boat has to sit "above" the fenders, the height of the boat's bottom above level ground is a major concern to allow launching at low tide.
Thanks.

[DayTripper]

I'm going to start looking for a used trailer for the flat bottom jon boat that I'm building. When a boat is sitting on its trailer, what is the typical height that the bottom is above the ground for easy launching off a boat ramp?

For future lurkers who might be interested in the answer to my question.

Just returned from a place that sells new and used boats. There were quite a few used boats on trailers, probably there for maintenance or repair.

Measured the height from the ground to the bottom of the transom. All were V bottoms so height was from the ground to the bottom of the V. The heights varied from 19" to 24" with about 21"-22" being common.

Just sharing info that I collected.

[John Meachen]

One point that hasn't been raised is that there are no dynamic advantages to having the boat higher than it needs to be when travelling at highway speeds.I can't think of any other time when high has any good points either.

[jpb54]

BTW, what are the hard plastic covers made out of? Any links to samples? Thanks.

Composite deck boards or composite 1 x 4 screwed to the top of the bunks works well .Also on the side rails .