question on scooter boat build

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Kevin Morin
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Location: Kenai, Alaska

Re: question on scooter boat build

Post by Kevin Morin » Wed Mar 16, 2016 9:59 am

Travis,
First, if you have a sketch of the transverse frames that you're describing, doesn't have to be the final, just a look at what you're describing it would help our discussion a lot.

Next, I'd say that from the CL of the boat or 42-43" from the sides, I'd recommend more like 1" of camber at the minimum, and 1-1/4" or 1-1/2" would not be out of line either. I'm not sure how that translates to the full deck beam depth? but it seems to add some depth?

I think that layout drawing is an important one for you to do this would confirm the longs' depths too.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

twaite
Posts: 129
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Re: question on scooter boat build

Post by twaite » Wed Mar 16, 2016 7:30 pm

Kevin,

Here is what I came up with adding a 1" camber:

Pontoons: 30" (bottom) Longitudal located CL (15")
Tunnel: 24" longitudal located at CL (1')

Scooter lofting.jpg
"This is in no way to scale as I do not have cad software but I hope it will show you how the 1" camber came out."

The measurements shown are at the full depth/length Longitudals as per previous framing discussions. The measurements are from drawing the section out on a flat board...

It does not show as much of a camber in my hogged drawing :D :D but it was quite noticeable on the drawing... I am learning
Capt. Travis

Kevin Morin
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Re: question on scooter boat build

Post by Kevin Morin » Wed Mar 16, 2016 8:06 pm

Travis, looks good to me? If its not to scale, where did you get dimensions? Did you draw it full size, measure then make an image to post? I see where you drew it out yourself. Good to do, and did you just bend the batten over the distance of where the 'expanded' circle points? Just seeing how you go the info? (edited from earlier post)

If so, then the 'true length' of the outboard sides can be directly measured off your drawing to use for planning the outer hulls' outer topsides?

I guess I forgot the tunnel is only 4" deep! Seems like it could be deeper? I will hazard a guess that the water will come out of that shape directly horizontal (near flat) with the tunnel top and that is where your cav plate & hydraulic jack will be toying with the running elevation?

IF you've done the boat (hull metals) work sheet and added your engine and rigging to get all up wt of 1,200 or 1,400 lb.???? have you figured where you will sit in the water? Displacement is done by wt of water = wt of boat. So you figure the volume of the boat for each inch it sinks in the water and convert that volume to water wt- until it equals your boat- that is how many inches deep the boat will sit at rest.

Did you ever mention where the waterline is drawn on the original plans? How far is the wooden version transom above some reference point? Like the deck, or the tunnel top or the side hull bottoms?

There are formula's online to convert water wt.s to volumes to allow you to figure your at rest depth (draft/draught/keel depth). A 12" x 12" x 1" deep path of hull (one board foot) of water weighs 0.036127lb. So if the bottoms are 2.5' wide (or 30") and there are two of them 60" wide and about 15' or 180" long (they're longer but we're just guestimating for discussion) then one inch immersion is 400lb of buoyancy/flotation/lift. So we can figure the boat is going to draw about 3 inches at rest, and that might be deeper aft that at the bow due to the engine, depending on what you put forward. IF the seat/console/fuel are roughly amidships then they pretty well push straight down- not by the bow or stern.

NOTE: because I shortened the bottom length figure due to not seeing the plans in hand; the figure of 15' of waterline may not be valid, making my guesitmate off. The bow ramps upward in the last few feet, so the figure of waterline length may be more like 16' or longer? IF so, each inch will float more and the boat will draw less. That is why I was encouraging you to make the tables of wts, aNd to consider figuring displacement.

So the transom I drew- measured 19.5" above the bottom of the side hulls, will be 3-3.5" too deep and needs to be raised at least 3" in the welded parts. The hydraulic lift will get another 6-8" up so that should be good enough even if this hull produces a rooster tail, which I don't see it doing at all.

The reason to mention this is that you may want to (now) scale up your design? IF the 20' break is back in the tooling set available? and the 20' sheets are being planned?? Why not consider 20' side hulls and add a little scale to the entire boat? NOT saying you need to but once you do the displacement estimation you may want more hull -all around?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

twaite
Posts: 129
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Re: question on scooter boat build

Post by twaite » Wed Mar 16, 2016 8:32 pm

Kevin,

Yes I did do a full size drawing and that is were I got the measurements from.

Scaling up:
Was planning on the hull length of 18'6... I to thought why not just go 20' and 7'6 on the bottom but I don't understand how to figure out if the boat will handle well as original plans as per designer are:
16' length
6'10 beam

Waterline:
There is no reference on the plans as per waterline except the list draft of 3 inches as per original plans.
Capt. Travis

twaite
Posts: 129
Joined: Sun Aug 10, 2014 9:38 am

Re: question on scooter boat build

Post by twaite » Wed Mar 16, 2016 8:52 pm

Draft:
Figures showed
LWL: 17
Beam:5.5
Lbs:1200

Draft: 2.5"

Displacement:
LWL: 17'
Beam 5'.5
Hull depth: 12.5"

=5900 lbs. displacement in saltwater, sounds high to me :shock: :?:
Capt. Travis

Kevin Morin
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Re: question on scooter boat build

Post by Kevin Morin » Wed Mar 16, 2016 9:24 pm

Travis, lengthening a straight hull won't really do much to the boat. It run flatter- that is the longer shape, with the same stern will have more 'bow' to lift to the lever arm (moment) of the bow forward the engine is greater- and that will keep her down more. The speed will increase a little both from the running waterline and the increased "burden area"- less to lift per sq. ft.

The turning will suffer a bunch- the smaller boat, once on step will turn inside the longer boat of the same shape. Not sure how high speed turning is really very important? AT speed you're not running a slalom or weaving in an out of pilings so, the longer turns aren't going to be a big deal -IMO. You do know this shape will turn almost flat? It won't heel like a V where the inside chine dips, the boat heels/rolls down by the inside of the turn..... this boat's shape is going to perform with much less heeling in turns. So making it bigger won't turn any better, but its mainly shaped to make a wave-free work boat in shallow water- right?

The last item is windage, even if the hull is low to the water, with the engine tucked inside the two side hulls low speed steering in tight quarters is somewhat 'dampened'. The tunnel will resist having her head pushed sideways in a breeze but, there's not real keel except the tunnel sides so the breeze will swing her at low speeds. Regardless if she's 16 or 20' long this will remain.

The prop wash is pushing against one vertical hull side AND pulling the other one vertically oriented through the water. So my guess is this boat isn't going to be all the good in very tight parallel parking spaces? However, most boat owners get used to 'jetting' the engine a little to push the stern around in "nudges" that get the job done; if they're driving jets, rafts, scow shapes and this is like that class. I'm not saying this boat won't maneuver, just that it's not going to be as agile as lots of boats with the engine aft the entire hull- giving some very good steering characteristics. You could view the two side hulls aft the engine as (shallow) rudders that are always straight ahead?

I was remarking about the scaling because the 20 sheets seem like they're back in the picture with a 20' brake to shape them? What about your patterns? Not sure of their since/LOA/scale to the drawings? Are your patterns for a 18'6" boat? You'd have to (partly) redraw the bow curve shapes to scale up, might just add a few inches on the 'bow end' of those curves? Fair them farther up a few inches in depth and a foot or so in length?

cheers,
Kevin Morin
Kenai, AK
Kevin Morin

twaite
Posts: 129
Joined: Sun Aug 10, 2014 9:38 am

Re: question on scooter boat build

Post by twaite » Thu Mar 17, 2016 4:12 pm

Kevin,

I Scaled up the original dimensions from:

Original:
Length: 16'
Beam: 6'10

Scaled up:
Length 18'6
Beam 7'9

I don't feel going to 20' length would be an issue however widening the bottom anymore would put the beam over 8' and I didn't really want all the seems topside, with 93 inches I will have one seem Down the CL unless it would be better to run sheets from P to S.. I am not sure what layout would be better for strength or if it makes a difference...

Couple of Question on Stern/motor board:

You suggested to use 1/4 plate for Motor board,

Should I also use 1/4 plate to close in the entire stern (transom)... one piece and then build motor board as per your drawings?

Also what are the recommended (proper way) for framing the motor board (in your drawings I noticed a few strips to be welded in-between the two clamping plates that make up the motor board) ?

Also any recommendations on assembling it ?

Thanks
Capt. Travis

twaite
Posts: 129
Joined: Sun Aug 10, 2014 9:38 am

Re: question on scooter boat build

Post by twaite » Thu Mar 17, 2016 7:13 pm

Kevin,

Below is the answers to the questions from a previous post:


[quote="Kevin Morin"]Travis, here are some sketches to discuss the transom/engine mount


Not shown, below decks at the interior line of the two hull's inner vertical planes; need some stiffeners and plates to weld the deck to -keyhole or pocket welds (some call these top down welds 'socket' welds but that term refers also to some pipe fittings that are welded and can be very confusing). The gussets would be welded to the deck on top of 2" wide plates or deck doublers that were just 3/16" flat bar rounded forward end bars that were welded to the deck under the edges of the white side transom gusset plates shown.

Travis, this is the beginning no the end of the information on the transom- what is not taken into account?

#1 the bolt pattern for the hydraulic jack's mounting bolt pattern- is needs to be defined BEfore you build this or you'll end up with head aches.

Hole Pattern Posted


#2 the actual engine model and leg length so you know there is adequate side to side turning radius in the width of the turning area between hulls.

Yamaha or Suzuki 115 (both of which will have plenty of clearance, the prop will basically set past the actual stern/transom of the boat with set back in Jack Plate..


#3 the engine steering system connections- cable or hydraulic. Either way you'll probably want to plan a conduit inside the hull (below decks) to hose the cable out of the way, or tubing, and that has to come up to the engine in the correct location depending on whether its tubing or cable?

Steering will be Hydraulic
Capt. Travis

Kevin Morin
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Re: question on scooter boat build

Post by Kevin Morin » Fri Mar 18, 2016 11:06 am

Travis,
making a drawing of the boat's stern area from Profile View is going to be important. The reason is to see what is implied in mounting you hydraulic jack to the transom.

A) the ht above waterline of the transom should be 19.5" to the top of the welded aluminum.
B) the lean aft of 15 degrees can be increased 5 degrees if you want. The reason is ALL the outboard tilt adjustment is outward!!!! not under. MANY boats have large, heavy outboards and sit down by the stern, have a 10-12deg transom as recommended by many engine makers- and they porpoise due to lack of rake aft/lean aft/angle to the waterline of the engine mount.

Ask yourself this question; from the fully 'tucked' position of the engine trim tilt- what is the SOLE direction of adjustment? Yep- aft and UP. SO what if lean the transom too far aft? Trim it! you've got about 10-15 degrees of trim but not one degree of tuck! my take
C) when the waterline is drawn in relation to the deck line, you can draw the transom 'box'/structure about 2" thick (I've done them much thicker and they work fine) and now plan the HydJack's bolts.
D) in the Profile view- you'll see if the bolts will all clear aBove the deck? OR, will the bottom two bolts in the pattern land below the upper deck line?
E) IF the lower two bolts land below the upper deck line- the bolts would end up inside the deck/tunnel top structure- not desireable. We'd like the bolts to all be outside an full hull penetration so they're not a leak path into the boat's deck/airvoid/sealed hull spaces.
F) When you do this Profile drawing, you'll locate the lower bolts, that will give you the point where your design has to accommodate the mount- and you have a couple obvious choices. #1 use a tapped set of holes with 1/2 plate 2"x2" blocks to take cap screws instead of through bolts at the lower bolts? #2 design some sealed access to keep the through bolt (if chosen) head accessible but sealed out of the boat's void/hull/under deck area or #3 build some sort of slotted mount for the jack that is mechanically supportive and only requires the upper bolts to secure the entire jack to the welded on hyd jack.

G) mixed news on the hyd jack and engine set back- the deck or hull design for this boat intended to have some 'hull' behind the engine. This was intended to keep the boat fro sitting down by the stern- in other words; like many modification we regularly see on large engine jon boats, bass boats, and other hulls of this class- the hulls' extensions Aft of the engine mount was to help keep the boat flat at rest. The engine is the biggest single wt to float and by having the hulls extend aft they act like add-on sponsons. By adding the hyd jack lots of that effect of leveling (at rest) the boat is being removed.

H) mUCh easier than cable! the tubes and all the electrical should be run in pipe/box/conduit/raceway under the deck, and inside the hull. This set of cables, engine controls, hydraulic tubes and all should be planned to run from your helm area down the leg of the console to the under deck fitting and into the conduit.

The conduit has to have curves that are wide/large radius enough to allow the cables/engine controls/steering tubing to bend but not kink. Have to set them on the bench to test curvature OR ask manfacturer- min bend radius then you have to plan that curve below deck. This conduit should be seal welded to the deck at both ends_ SO..... technically its 'outside' the hollow bottom below decks. The conduit may fill with water if you do a poor job at the two ends of sealing it.... but that water can't get into the hull. Further this conduit can be blown clean of water by using shop air at one end for periodic maintenance.

Image
The photograph above shows a controls conduit- what a conglomeration! First the pipe is 3" sched 40 because that size would all the 'plug end' of all the engine cables to fit through the pipe. The plugs on the end of pre-cast cables are often much larger than the rest of the cable- but if you can't thread the plug end through a conduit- the conduit is too small.

Next I had a short bend segment of pipe lying around so I just spliced the pipe bend with stub ends to two other short pieces of 3" and that gave me the main run and the bend gave me the offset from one side of the hull (where the helm was to be located) to the centerline.

The ends were low cost bends. Here is where my problem came from- that made me weld up the ends as square 'ducting' 90's. All pipe bends at different radii, where smaller pipe bend tighter than larger. I found that long radius cast butt weld 90's in 3" 6061 pipe were more than a day's wages . Bending pipe in a single shot this large is tricking due to the details of benders- and is also expensive.

So I made two side curves of the radius I needed- and have confirmed all my engine/throttle cables would bend round/inside. The I made the square duct like end 90's and butt welded then after some anvil work to the pipe. I did ream the pipe wall carefully so there are a smooth transition inside and no shoulder to hang up the bundle of cables when pulled through.

I'm not sure you have the depth to make this deep a curve? You may need to make something different to work for you boat? I'm just showing an example.

Image
Above the butt weld between the conduit's pipe segments. The entire conduit was sealed and air tested to 10psi so there was no chance of problems leaking into the bilge.

Image
A little bit of gray-scale to make things hard to see! The conduit runs from the lower right in the picture above, to the middle left and is mounted by a series of welded 'tabs' in both directions and welded to both the structural longs and the hull in a few places.

The small dia pipe that runs across the hull from lower left to upper right is where the cabin heater fuel (propane) line runs. The tank is in a stern locker, vented and outside the cabin and the conduit allows the hose to be fed under the deck and pulled up into the cabin to run the little heater.

The other pipe is the fuel line conduit, he tank on this skiff is incorporated into the cabin's forward bulkhead so the tank draw fitting is inside the cabin with a shut off valve. From the shut off valve the fuel hose goes down into the lower horizontal pipe (in this photo) and turns up in the fuel locker at the stern.

Hope these remarks help with your planning?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

twaite
Posts: 129
Joined: Sun Aug 10, 2014 9:38 am

Re: question on scooter boat build

Post by twaite » Fri Mar 18, 2016 5:40 pm

Kevin,

Should I frame up the stern section with 2x3 extrusion and cap it with 1/8 on both sides.... I am not sure how to even begin to draw this as in the plans the motor clamp board slides into the framing system. Should the stern section be 1/4 or 1/8
dsn-sctlb.jpg
Red outlined areas are what I am asking not sure how to handle the framing here.
Capt. Travis

Kevin Morin
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Location: Kenai, Alaska

Re: question on scooter boat build

Post by Kevin Morin » Fri Mar 18, 2016 5:51 pm

Travis, generally when making metal boxes the sides are plenty enough framing.

You have circled two different framing areas. One is the after end of the hulls- these can just be 1/8 sheet edge to edge on the four sides of the ends of the hull. Use the types of chine/hull/sheer joints I show in the other thread- inside edge to inside edge- will work fine with a single sheet of material -no extrusions involved. Nice to butt the three hull longs to the transom end.

The engine mount has already been sketched- the frame is a 1/4 plate touching the after edge the deck. Then 1-1/2" spacers and extrusions and then another 1/4" plate touching as far down the 'tunnel' back plate as it "lays out".

As the inner hull sides will reach the deck, and be welded to the deck, the two side gussets need only have a hull/deck doubler plate (1/4" x 2") welded flat to the deck to distribute that point load and the side gussets can weld to the sides of the previous 2 1/4" plates and the deck- on top of the gusset?

was my drawing confusing? All the engine pull; aft ..... and torque around the mount...... and thrust forward are expressed on the two inner hull sides as 14"-15" tall 18' long I-beams!!!!

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

twaite
Posts: 129
Joined: Sun Aug 10, 2014 9:38 am

Re: question on scooter boat build

Post by twaite » Sat Mar 19, 2016 4:08 am

Kevin,


Motor board:



The engine mount has already been sketched- the frame is a 1/4 plate touching the after edge the deck. Then 1-1/2" spacers and extrusions and then another 1/4" plate touching as far down the 'tunnel' back plate as it "lays out".

Understand the concept of this and agree...

As the inner hull sides will reach the deck, and be welded to the deck, the two side gussets need only have a hull/deck doubler plate (1/4" x 2") welded flat to the deck to distribute that point load and the side gussets can weld to the sides of the previous 2 1/4" plates and the deck- on top of the gusset?

Could you explain the Hull/deck doubler plate (1/4" x 2") welded flat to deck? Is that a 2"x2" angle?


Thank you for the post on the pipe bending and assembly, that will help a lot and I must say it was a great idea...


xverse and full longitudal question:

I have noticed some builders cut circles out of the Xverse and the Full longitudals and I am assuming that they do it to lighten up the hull weight.. Is this ok to do, if so what is the max amount that can be removed?

Thanks ,
Capt. Travis

twaite
Posts: 129
Joined: Sun Aug 10, 2014 9:38 am

Re: question on scooter boat build

Post by twaite » Sat Mar 19, 2016 5:52 am

Here is a picture of a engine mounted as per original wood plans ,
Scooter engine mount.jpg
as you can see there is plenty of clearance..... just updating from previous post
Capt. Travis

Kevin Morin
Posts: 699
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: question on scooter boat build

Post by Kevin Morin » Sat Mar 19, 2016 1:21 pm

Travis, the cutouts will lighten up the build somewhat, they also allow bilge air to circulate and dry out any condensate and to reduce hot and cold spots due to sun and water temp. differentials. All good things.

The margins between a cut out and the edge of a structural element's outline are usually defined as Xthickness from the nearest point. Say you have a 1/8" hull long, and plan cutout? Then 15x the clearance to the nearest edge is 1-7/8" from the nearest edge- call it 2" from the edge. So the longs are 14" tall and 4" less is 10" what is the area of a 10" circle in 1/8" (Pi * R^2 = A so 3.14159 * 25= 78" area. That's about a pound per cutout. Say they're spaced 4" apart fore and aft- and you've got several like this? So you'll save 25 lb? Not really worth taking time to do.

Then when cutouts are made, depending on the material- and location some need to be lined with bar or pipe segments to retain the panel stiffness AND some places need a vertical bar to retain the panel's vertical moment- conclusion? Not worth the time in your size and scantlings.

I'll try to sketch the other questions later.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

twaite
Posts: 129
Joined: Sun Aug 10, 2014 9:38 am

Re: question on scooter boat build

Post by twaite » Sat Mar 19, 2016 2:40 pm

Kevin,

Sounds just as I thought.. thanks for the clarifications.. After I thought on it for a while it sounded like a lot of work in this small of a build...

Look forward to the drawing, thanks again for all your help as it would have been a mess without it... I am really learning a lot...

Regards,
Capt. Travis

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