Cross member spacing

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JLester273
Posts: 241
Joined: Wed May 10, 2017 10:23 am
Location: Cincinnati Ohio

Cross member spacing

#1 Post by JLester273 » Wed Jul 19, 2017 11:31 am

Since I will be rebuilding My Harris I want to do it once and be able to do what I want from now on with the pontoon.

Currently I have a 75 HP on it. It was originally rated for 70 according to the old Ad Harris sent me.

For now the power is fine. But I thought in the future I might want to do more to this boat (bigger toons, maybe a Tritoon conversion) I don't know for sure. Just thinking out loud, or in type rather.

So my current spacing on my cross members is 24" it is a 24 ft boat but only has 20 ft on the deck. I am planning on extending this. Perhaps the who length if not at least to the front of the pontoons. My thought is to reinforce both the front and back of the boat. The front to make it easier to use the winch when getting it on the trailer. As it is I cant do much without trying to deform the front rail. This seems less critical to me than the back.

If I decide later to repower it I would like not to worry about having to take the deck up etc. If adding strength back there is the main issue.

I have seen it don't on third toons. And that may be great but what about more support in the stern? An extra cross member or two can't hurt I'm sure but does it change anything?

So how are you higher horsepower rigs setup with the rear cross members? What should I do now while I have everything apart in the chance I may do this later.

Again thinking out loud about what to do to this thing while it is apart.
My rebuild thread.
http://www.pontoonforums.com/viewtopic.php?f=16&t=24807

mrlouis
Posts: 32
Joined: Fri May 01, 2015 4:27 am

Re: Cross member spacing

#2 Post by mrlouis » Wed Jul 19, 2017 4:25 pm

putting the cross members closer together will help but you still need more buoyancy back in 1988 most pontoons were 20 " maybe 23 " tops which is the reason most pontoons of that day could not handle larger horsepower motors and came with no more than a seventy HP
adding a third center toon will help but it still won't allow a large HP if you have the smaller outside toons

Bamaman
Posts: 3630
Joined: Fri May 06, 2011 1:44 pm
Location: NW Alabama--Tennessee River

Re: Cross member spacing

#3 Post by Bamaman » Wed Jul 19, 2017 4:35 pm

A 24' boat with only 70 hp capability tells me you may have small diameter toons--perhaps 19".

If your needs include more speed and capability to handle more people, you'd probably do best to dress up your current rig and put it on the retail market.

The more modern pontoons are now equipped with 25" toons and they're another 6 inches wider than your boat probably is. They're just inherently more seaworthy.

Throw a third toon, lifting strakes and undersheeting on a 115 hp or 150 hp boat, and you've got another animal. You just wouldn't believe how smooth my 24'/150 hp/tritoon rides and how quiet it is in the water.

And if it's at all possible, every tritoon owner should put all the horsepower his pocketbook will allow on any new boat they purchase. There's a big difference between 115 and 150 horses.
'12 Bennington 24' SSLX Yamaha 150

JLester273
Posts: 241
Joined: Wed May 10, 2017 10:23 am
Location: Cincinnati Ohio

Re: Cross member spacing

#4 Post by JLester273 » Thu Jul 20, 2017 6:36 am

Ah so there is why they have the capability. I was thinking strength. Yes I think my outside toons are 19-20 inch toons. I will have so much into this at the end of the rebuild I have thought eventually of changing the toons too (just later) I know that can be done. I'm just thinking for the future if I decide to (or need to) repower it and I haven't added the proper support back there I'll be out of luck.

Of course for now I am very happy with the speed. So I am not sure if I really will do that. I'm just don't want not thinking of it now being the only reason I can't later if I change my mind.

I know it sounds crazy probably to not just sell it and buy a different boat but My situation is a bit different then most with this pontoonstuff rebuild.
My rebuild thread.
http://www.pontoonforums.com/viewtopic.php?f=16&t=24807

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rancherlee
Posts: 577
Joined: Tue Jul 13, 2010 5:59 am
Location: Eveleth MN

Re: Cross member spacing

#5 Post by rancherlee » Sat Jul 22, 2017 10:30 am

With a center tube, spacing is less of a issue since the center tube basically becomes a giant transom pod and links the engine to ALL the cross members instead of just the rear 3 or 4 cross members. That said, I added an extra cross member between the front 2 and the rear 2 when I upgraded the tubes on mine since it had 24" spacing.

When it comes to HP and Capacity rating Tube diameter effects Capacity a lot more than HP rating. The HP rating is based mostly off the length and number of tubes. When I had 2 factory 19" tubes Calculations showed ~85hp and 8 people (factory rated 75hp 8 people) adding a 3rd 19" center tube calulated out to ~125hp and 9 people (50% more power/12% people vs 2 tubes) Now with my new 25" tubes the the calculations show 155hp and 13 people (24% more power/44% more people vs 19" tubes). Most pontoons I look at follow the same pattern with the center tube option offering only 1-2 more people but 50% more HP
1988' Kennedy 20' "Haley's Comet"
Rebuilt 2016 with 25" single strake outer tubes and a 25x23" straked U-tube
2003 Suzuki DF140 - Yamaha 9.9HT kicker - 39.1@6300rpm

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mpilot
Posts: 313
Joined: Mon Mar 14, 2016 11:56 am
Location: Lake Murray, SC

Re: Cross member spacing

#6 Post by mpilot » Mon Jul 24, 2017 12:13 pm

A friend did a custom rebuild and added cross members to the back of a pontoon to put a bigger motor on it. It had 25" toons and he also had a new motor pod built that was similar to what Bentley uses and will handle up to a 250 HP. I think the motor pod was 8 feet long if I remember right. At the rear he actually added square aluminum tubing since per the recommendation of the fabricator along with 4 inch lifting strakes on both sides of the toons. He put a tower on it and two captains chairs, hydraulic steering, and a manual jack plate to raise the 225 HP he put on there. Before he sold it, we had it running consistently in the 60's, but I think with a little motor tuning, playing with the jack plate, and trying some other props we probably could have hit 70 on the boat, but it would have been scary. Fastest boat to plane I have ever ridden in...would go from a rolling start to 30mph by the time the GPS updated. It has held up well and after the new owner added some new furniture which weighed the boat down it runs in the high 50's now the last I heard.

JLester273
Posts: 241
Joined: Wed May 10, 2017 10:23 am
Location: Cincinnati Ohio

Re: Cross member spacing

#7 Post by JLester273 » Mon Jul 24, 2017 2:11 pm

I was actually looking at pontoons over the weekend. I found a set of 27 inch logs that where about 2600 for the set. That didn't seem to bad. I think that would probably be my first change after the top side is done. That or the 25 inch. Only reason I saw really to go to the 25 inch over the 27 was that there were 25 inch center logs readily available. I didn't see ones for the 27 inch diameter. That seem pretty reasonable for new logs. And once I have everything else done I figure I might as well....Custom pontoon ground up. LOL

We will see. Still dreaming and planning. LOL
My rebuild thread.
http://www.pontoonforums.com/viewtopic.php?f=16&t=24807

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