Short Shaft Motor or Long Shaft Motor for Zip, which one??

Outboard designs up to 14'

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Thomasbuilt
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Short Shaft Motor or Long Shaft Motor for Zip, which one??

Post by Thomasbuilt » Fri Jan 21, 2011 7:49 pm

I was wondering which motor is better for the Zip??

I'm sure old vintage engines that are long shafted are more common.

Just would like to know which preforms better, may a one helps the boat planes out quick with one or the other, I'm not sure just throwing some thoughts out, any help??

thanks for any info.

upspirate

Re: Short Shaft Motor or Long Shaft Motor for Zip, which one??

Post by upspirate » Fri Jan 21, 2011 8:15 pm

Vintage motors are normally short shaft 15 3/4" inches in the 30-40 HP range

Later models are normally 20 3/4 and are easier to find,parts etc,they have electronic ignition,different ratio oil mix etc,better for salt water corrosion resistance.

Either will work fine as long as the transom is the proper height for the motor used.

They changed the way they rate the HP...can't remember when they did this, so a newer 40 may not put out the same as an older one.

All this is comparing motors of similar condition

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vupilot
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Re: Short Shaft Motor or Long Shaft Motor for Zip, which one??

Post by vupilot » Fri Jan 21, 2011 9:44 pm

The power rating was changed in the early 1980's I think 83. The power is now rated at the prop shaft not the crankshaft. So a newer 35hp should push a Zip along about as well as a pre 1983 40hp, all other variables being equal.

As for short or long shaft, its completely personal preference. Just build your transom to suit which you decide on. The transom height should equal the motor shaft length. 15" shaft=15" transom. 20" shaft=20" transom.

Having built a short shaft Zip I think its slightly easier to hook up steering and other controls on a long shaft because the motor is up higher and the steering (especially the tilt tube type) is up higher and out of the way of the motorwell and you will not have any clearance issues to deal with from the steering rod and link.
In the picture below you can see I had to cut out a clearance port for the steering link in the motorwell side. To get around this with a short shaft you can use a motorwell mounted steering bracket or make the motor well wider.
Launch 003.jpg
If you look at the link below you can see on Tom Drake's Zip with a long shaft the steering is all above the deck and motorwell. A easier installation in my eyes (T. Broadlick Photo)
http://picasaweb.google.com/Buckeyesmit ... 7786680802

Again its all personal preference and each work equally as well performance wise. Long shaft motors do seem a bit more common but I really wanted the low sitting motor and the petite look of a short shaft.

-Chris

John K
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Re: Short Shaft Motor or Long Shaft Motor for Zip, which one??

Post by John K » Sat Jan 22, 2011 6:28 am

vupilot wrote:The power rating was changed in the early 1980's I think 83. The power is now rated at the prop shaft not the crankshaft. So a newer 35hp should push a Zip along about as well as a pre 1983 40hp, all other variables being equal.
If I remember right the older Mercs were always rated at the prop and Johnsons/ Evinrudes were rated at the crank. That is why Mercs would also outrun the others.

I don't know where you could find this, but that is what I remember.

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galamb
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Re: Short Shaft Motor or Long Shaft Motor for Zip, which one??

Post by galamb » Sat Jan 22, 2011 9:34 am

So many versions of when - so I'll add my 2 cents.

It was the early/mid 80's when outboards began to see some Shaft Horsepower (SHP) ratings instead of Brake Horsepower (BHP).

Merc completed the total transition in 1986 when they launched their entire new line of outboards. To keep in step with them OMC completely followed suit - so by 1986, at least all North American produced outboards (Merc, Force, Johnson/Evinrude) were rated in SHP.

Some were new designs, others were simply "rebadged". The general rule of thumb with outboards is that the SHP will be about 10'ish% less than the BHP rating. (It can be calculated but there is no "one equasion fits all" rule)

So in a couple notable cases, the 40 Merc became the 35 and the 200 Johnson became the 185 (an odd horsepower that OMC scrapped a couple years later). So while the 1983 200 Johnson and the 1984 185 Johnson were mechanically identical (ditto the 40 and 35 Mercs), the new "stickers" simply reflected the rating change.

As a side note, I don't know of anyone that could "feel" the performance difference between a 35 or 40 horse motor on a given boat. If you took off the decals and told them it was a 50 hangin' on the back, they would take your word for it. In the 30-50 horse range moving up or down 10 horses results in "no noticable" difference. Above 200 horses even a 50 horse change would barely make a difference, so when comparing a 40 BHP compared to a 40 SHP the only thing that should concern you is 1) can I get parts and 2) which will look "cooler" on my build :)

Until the EPA got into the mix and started really regulating outboard emissions, Merc tended to "under-rate" the horsepower of their motors so that they would always come out on top of "head to head" tests. As an example, most 90 Merc's built between 1985-1994 actually would measure at 100 SHP if they were dyno tested.

One note on transom height. The coastguard rates a boat with a 20" transom "safer" than one with a 15" transom. That will allow you to carry more weight or hang a higher horsepower motor on the 20-incher and still be in compliance with the guidelines.
Graham

Yes, Plywood is "real" wood :)

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)

Thomasbuilt
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Re: Short Shaft Motor or Long Shaft Motor for Zip, which one??

Post by Thomasbuilt » Sat Jan 22, 2011 9:06 pm

Thank you guys for setting me straight on the motor info, like always I learn alot more than I thought I should know.

Even thought the plans call for 40hp max, I've seen pics of 45's and one 50hp on the Zip in customer photo section, but I notice the plans have a insert which may be something they send for all outboard motor boat plans stating how thinck the transome should be all the way up to a 85hp. I'm sure that is just common boat building methods. There is no way you can put anything bigger than a 50hp on a 200-300lb hull?

Have a good one and thanks to all you guys for the help.

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galamb
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Re: Short Shaft Motor or Long Shaft Motor for Zip, which one??

Post by galamb » Sun Jan 23, 2011 8:13 am

The Coastguard has different formulae for calculating the maximum safe horsepower for a given hull and it is based on dimensions, not the hull weight.

Most "homebuilt" outboard powerboats will be based on a hard chine, v-bottom design.

So you can use their basic formulae to calculate what they figure is "safe" (and if you don't meet their regs it's near impossible to insure the boat and many States/Provinces won't register it).

You will need a couple measurements to figure max horsepower. First you need the boat length - measured from the upper tip of the bow straight back to the exact middle of the transom (often referred to as "length overall" or LOA) - this is usually a different number than either the waterline length or centerline length.

The second number you need is the transom width. And that has to be measured along the upper edge (top) of the transom - in that case it doesn't matter if the transom flares in or out at the top (most hard chine boat chines are their widest at the top) - whatever the measurement is accross the top is what they use.

If you build your Zip exactly to spec it would be 14' 4" long and have a beam of 5' 9" (and while I don't have the plans to look at, have to assume that the transom is 4-6" narrower than the widest part of the beam - so for the sake of doing the calculation call it 5' 4").

Now here's where you get the calculator. The first thing you calculate is the "factor" which is simply the length X transom width -

(these are coastguard numbers not mine :))

(14' 4") 14.333' X (5'4") 5.333' = 76.437

Round your factor to the nearest whole number - 76.437 = 76 (76 is your factor).

Now you use one of two formulae depending on whether you have a 15" or 20" transom.

If you have a 15" transom -

Multiply your factor by .8 = 76 X .8 = 60.8
then subtract 25 = 60.8 - 25 = 35.8
then raise it to the nearest multiple of 5 = 35.8 raised to 40

So for a 15" transom with the measurements of the actual hull, the max horsepower would be 40.

If you have a 20" transom -

multiply your factor by 2 = 76 x 2 = 152
subtract 90 = 152 - 90 = 62
then raise it to the nearest multiple of 5 = 62 raised to 65

So for a 20" transom, all other measurements the same, the max horsepower would be 65.

(these formulae only apply to V-bottomed boats with factors above 52 that have either a 15 or 20 inch transom)
Graham

Yes, Plywood is "real" wood :)

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)

Tom Drake
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Re: Short Shaft Motor or Long Shaft Motor for Zip, which one??

Post by Tom Drake » Mon Jan 24, 2011 6:40 am

You ask for the time of day and you are told how to build a clock. Your question was answered by Warren and Chris in the first two post. It's a matter of choice. As an RC flyer, which do you prefer--JR or Futaba ? Same type of question. But, the side trip was interesting. In the late 40's, we owned a Mercury Hurricane 10. The street story was that it equated to most 15HP outboards because Mercury rated their outboards behind the gearbox at the prop shaft while others rated infront of the gearbox. That was a simple answer that worked at the time. 10HP was the max for a racing hydro class at the time and Merc dominated that class.

Thomasbuilt
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Re: Short Shaft Motor or Long Shaft Motor for Zip, which one??

Post by Thomasbuilt » Mon Jan 24, 2011 8:20 am

LOL, your right. I know how to build a clock and a motor now, :-). Thats what I love about this forum. You guys answer every question and make me think of more questions I should of been asking myself. Thanks again for all the additional info, it is alot of help. Have a good week.

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