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Arima's transom

Started by Yachter Yat, March 07, 2018, 04:08:25 PM

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Yachter Yat

 
    Call it curiosity, but if Arima's transom was "squared-off", do you suppose it would result in the aft section being lighter?  Would it provide more buoyancy?  Wouldn't it also provide more platform area by virtue of reversing the angle of the sponsons?   I mean, the motorwell and bait hatches would be pushed back, correct?  As designed, the area between the sponsons is "water".  If that water (being fairly heavy)  were displaced with seemingly lighter hull, wouldn't it be inherently forced to ride higher?  I don't have a photo of it, but I'm picturing something like the transom of my 1977 17 foot Silverline Nantucket runabout.  I had a Johnson 150 on that thing.

   Here's something else that has my curiosity up:  If a boat has a transom that is angled "forward", doesn't that mean that as it is forced deeper that it displaces "less" water than a boat with a transom that is angled "back".  It just seems to stand to reason that if a transom is angled "back", then the deeper it is forced the more water it will displace..............no??   Okay, I know, it wouldn't be an Arima.  Just asking. 

Yat

   As an addendum to the above:  May I be honest here?   Okay.....sometimes I think this could be a viable consideration for the Sea Hunter.  Perhaps more buoyancy and certainly more platform. 
History is not the past; it's the present, as we all carry it with us......James Baldwin    
16 SC/Honda 60  (sold)

Fisherdv

#1
I kind of think that the 9x12 trim tabs I installed take up some of that "water" space you mention between the sponsons. Although they probably don't add any buoyancy at rest, they sure add lift at speed. The size of them takes up a good amount of that empty space almost like filling in the gap you mentioned. Supposedly having the motor forward like that adds to the efficiency of the hull and being able to run a lower HP motor. Although I have also thought about what the boat would be like being a full 15'11", or actually having the thrust from the motor back there. I mean, can we technically call a 16 a 16 with the transom and motor at more like 15 ft :shrug9: I actually think if the transom was squared off like you mentioned that the smaller boats like our 16 may feel bigger and less prone to porpoising. Kind of like a boat with that extended motor mount. But, like I said I think it was built this way for easy planing and efficiency with smaller motors and also to help with the boat slip costs that charge by "overall" boat length and maybe even registration fees
2018 Sea Chaser 16, Honda BFP60

Fisherdv

Quote from: Yachter Yat on March 07, 2018, 04:08:25 PM


   As an addendum to the above:  May I be honest here?   Okay.....sometimes I think this could be a viable consideration for the Sea Hunter.  Perhaps more buoyancy and certainly more platform. 

And stretch the hunter platform by 5, and..........wait a minute......that's your line :jester:
2018 Sea Chaser 16, Honda BFP60

AJFishin

Kind of sounds like you're describing a Defiance boat?  :shrug9:
'96 Sea Ranger 19, 2016 Mercury 115 EFI CT (115F231D) 
'96 Sea Chaser 16, 2019 Suzuki DF60AV (Sold) 
'87 Sea Chaser 17, 1987 Johnson V4 90 (Sold)
My YouTube channel: youtube.com/socalseachaser

Salmon King

Yat...you could always modify your boat and find out... :biggrin:
PLEASE...Fly your flag Proudly, and remember to thank a Vet!
2011 14' Sterling
9' Pontoon (Bismarck)
8' Pontoon (Hood)

croaker stroker



You would loose some side to side stability.
1987 - 17' Sea Pacer - 2004 Evinrude 90 E-tec
1985 - 15' Sea Sprinter - **SOLD**

"Ex Tridente Pax". 🇺🇸

Redhawk

Probably not. What squaring off the transom would do is take that excess material from the indent for the motor, and put some of it elsewhere like for the reverse sponsons. Having a lighter transom could also affect the way the boat rides as the less weight there is aft, the higher the hull will ride, and if it is too high then you are going to get tossed around as it has lost most of its ability to punch through waves smoothly, which comes from the draft and weight of the whole boat but mainly the stern, as that is what's in the water when planing. I think. Just my  :twocents:
Sparhawk:
1983 Tiderunner 150 Cuddy
1995 Mercury 60 2-stroke
1984 Evinrude 6 2-stroke

Salmon King

Personally...I think it would be hard to improve on the ride and performance of an ARIMA.
PLEASE...Fly your flag Proudly, and remember to thank a Vet!
2011 14' Sterling
9' Pontoon (Bismarck)
8' Pontoon (Hood)

Chief of the Boat

Don't change something that is not broken. :twocents:

J Chaser

Sea Chaser 1511, Yamaha F70, Yamaha F6 kicker

Yachter Yat

      I happen to like Arima's transom.  I have no problem with it.  That said, if I had a dollar for every post I've read on this Forum regarding how Arimas were "butt heavy", I'd be dining with Bill Gates this evening.  Truth is; Arima's transom design happens to posses both positive and negative idiosyncrasies.  If you happen to be a major "fan boy" of this transom, then I don't really believe you'd like to hear what I have to say.  I'll leave it there. 

Yat

   
History is not the past; it's the present, as we all carry it with us......James Baldwin    
16 SC/Honda 60  (sold)

Markshoreline

After almost 40 years of production, Arimas are still on the water and are in great demand.  While there are always suggestions of how they could be improved no one has actually done so.  We are a community that comes together because of the great boats that we own and enjoy!  I just can't imagine a better boat for Puget Sound and occasionally the ocean with better fuel economy, passenger comfort, multipurpose use and resale value.  Yep, I'm a fan!
2002 Sea Ranger HT 21, Yamaha 150, Yamaha 9.9

Fisherdv

2018 Sea Chaser 16, Honda BFP60

Threeweight

Eliminating the notch wouldn't change the 17' and under Arima's being butt heavy.  To fix that, you need to go to a belly-mounted fuel tank.
Former Sea Chaser 17 owner
Defiance 250 Admiral, twin Yamaha 150's and T9.9

"Never turn your back on fear. It should always be in front of you, like a thing that might have to be killed."
       --- Hunter S. Thompson

Yachter Yat

   Sorry, but I must respectfully disagree.  IMO, Arima's hulls aren't really as butt heavy as some may suggest.  I think they're simply less buoyant than some of the more "conventional" squared-off transom designs.  For those who may have forgotten, this hull was conceived at a time in history when many of us were wondering if we would be able to get enough gas to go to work.  Consequently, Arimas were touted as being a fuel efficient boat that was capable of being run with low powered motors.  As it turns out, and from my experience at least, that's exactly what they were.......and still are.  In my mind, Arima's thinking may have been that the indentation between the sponsons (in a way) would serve to shorten a portion of the hull; thereby, reducing drag.  The hull would then gain-back the lost buoyancy (and lift) by extending those sponsons farther aft.  In other words, there would perhaps be less wetted surface when on plane.  Additionally, "clipping" the corners of those sponsons (on the angle that you see) would reduce that wetted surface even more.  We can go further and say this "sponson design" not only translates to efficiency at speed, but indeed, may also contribute to Arima's stability at rest.  Quite impressive, I'd say. 

   BUT.........like everything else in life; there's a trade-off.  Here's what I believe that is:  When you chose to remove a large section of hull (such as between those sponsons) you actually reduce the amount of buoyancy by the amount of water your NOT displacing.  The same is true when clipping the corners of those sponsons.  In other words, that is hull (that happens to be full of "air") that's not in the water....."holding-up"  the hull.  Next, when you decide to "angle-back" a transom......or portion of that transom, as in the case of those sponsons, then you create the potential for another problem.  And it's this:  As you add weight to the rear, and the hull goes deeper.......the boat actually gets "shorter".  Less length at waterline simply means less displacement, which means the hull  has less ability to support a given amount of weight.  Here's another way to see it:  If a hull had a square transom that was angled-back; then as it was pushed deeper it would displace more water, creating more resistance, and, thereby, would have the ability to support more weight. 

   So......are Arimas really "butt heavy"?  I honestly don't believe there that much heavier than any other boat in their class.  It's simply by design that they have a more limited ability to support the excessive amount of weight that we often see impose on them.  Arima's  hulls were designed to do the specific job of providing the highest level of fuel efficiency with the least of amount of horsepower, while simultaneously providing an unparalleled stability at rest...........a job these hulls have done exceedingly well. 

   So, I guess the question might be:  Is there an Arima that could benefit from a more conventional transom?  There may indeed be......and it could be the Sea Hunter.  After all, it seems being the smallest in the fleet would obviously make it the most sensitive to weight introduction.  Modifying that transom to something like my old 77 Silverline might be just the ticket for that boat.  Look back at pics of a Sea Hunter that's been asked to carry two motors, two batteries, full bait hatches, lead downrigger balls a fish cooler and the kitchen sink and you'll see what I mean.  Needless to say, that's much less of a problem for the bigger Arimas.   

    In the final analysis, I believe what it comes down to is, not so much Arima's transom weight, but rather, a certain amount of sacrifice in buoyancy in order to enhance performance in those other areas mentioned. 

Yat

     

     

   
History is not the past; it's the present, as we all carry it with us......James Baldwin    
16 SC/Honda 60  (sold)

croaker stroker

Quote from: Yachter Yat on March 13, 2018, 06:33:53 AM

   BUT.........like everything else in life; there's a trade-off.  Here's what I believe that is:  When you chose to remove a large section of hull (such as between those sponsons) you actually reduce the amount of buoyancy by the amount of water your NOT displacing.

    In the final analysis, I believe what it comes down to is, not so much Arima's transom weight, but rather, a certain amount of sacrifice in buoyancy in order to enhance performance in those other areas mentioned. 

Yat



Rather than looking at the Arima hull as having a section of the hull "removed"....Consider the sponsons having been added....providing more buoyancy.
1987 - 17' Sea Pacer - 2004 Evinrude 90 E-tec
1985 - 15' Sea Sprinter - **SOLD**

"Ex Tridente Pax". 🇺🇸

blindmonkey

The popular deep v boats of similar size in BC that have conventional transom designs have the same issue and some are much worse. There is only so much weight a small boat can handle.
Lorne
2013 17' Sea Chaser, Honda 90, Yamaha F8 SOLD
1994 Sea Explorer, Mercury 60, SOLD

Rokefin

Yep, not much you can do unless you want to move your fuel tanks, batteries, kicker......could really lighten the back end if you wanted to mount your main in the off the bow :facepalm:

Yachter Yat

   Croaker;  Yes, you would add buoyancy, but does the weight of those sponsons offset that buoyancy?  Keep in mind; those sponsons have a "negative" angle.......meaning they are angled "forward".  Remember.......the deeper you go...................

   Blindmonkey;  Having never been witness to that; I can't legitimately respond. 

   Rokefin;  Maybe, but how is it that we see these little C Dory 16's (only 6'-6" wide) with two motors hangin' on the back, sitting so high at the stern?

   And why was it that my old 17 Silverline (which, as I recall, wasn't as wide as a 17 Arima) could sit so high in the water with that mega 150 motor, 18 gals. of fuel, batteries and a bunch of other junk in the stern?   :shrug9: 

   I don't know why, but I get the feeling a guy like Threeweight is going to come up with a gaggle of geometric calculations in an attempt to dispute my suspicions......after which I will be forced to go into the garage and make a bunch of model boats that I'll have to then take into the bathtub, in order to test and disprove said calculations.  :jester:   Kidding aside, seems this might be an interesting conversation to have with marine architect. 

Yat

   



   
History is not the past; it's the present, as we all carry it with us......James Baldwin    
16 SC/Honda 60  (sold)

Rokefin

I can see how this debate can go in circles......I guess we have the Arimas because we like how they are, I'm sure some changes could be done to improve but I wouldn't want to sacrifice the stable fishing deck in any way....

We definitely would need some engineering insight to this.  Yat PLEASE no bath tub picks of experiments :wink:

Yachter Yat

   No bathtub pics?   Okay, but you must agree with me!  :jester:

Yat
History is not the past; it's the present, as we all carry it with us......James Baldwin    
16 SC/Honda 60  (sold)

Threeweight

Everything heavy (batteries, fuel tanks, engines, bait wells (if you use them), wash down pump, etc...) is all mounted in the stern of an Arima.  Therefore, they are butt heavy.

Moving the batteries forward and shifting 100# off the stern and up to the bow has a pretty huge and well documented impact on the handling of the boats. 

More planing surface to the hull isn't going to effect weight distribution.  It would help slightly with top speed, and maybe fuel economy,
Former Sea Chaser 17 owner
Defiance 250 Admiral, twin Yamaha 150's and T9.9

"Never turn your back on fear. It should always be in front of you, like a thing that might have to be killed."
       --- Hunter S. Thompson

croaker stroker

You guys be patient with Yat. He has been huddled inside for the past couple of weeks. Three Nor'Easters in a row !!

🤪
1987 - 17' Sea Pacer - 2004 Evinrude 90 E-tec
1985 - 15' Sea Sprinter - **SOLD**

"Ex Tridente Pax". 🇺🇸

AJFishin

Quote from: Croaker Stroker on March 14, 2018, 12:06:15 PM
You guys be patient with Yat. He has been huddled inside for the past couple of weeks. Three Nor'Easters in a row !!

🤪

Or he spent the night at a Holiday Inn. :biggrin:
'96 Sea Ranger 19, 2016 Mercury 115 EFI CT (115F231D) 
'96 Sea Chaser 16, 2019 Suzuki DF60AV (Sold) 
'87 Sea Chaser 17, 1987 Johnson V4 90 (Sold)
My YouTube channel: youtube.com/socalseachaser

Yachter Yat

    Got 16" of snow last week and another 21" yesterday.  Me and the Kubota just spent most of the day cleaning-up. :hoboy:   No Holiday Inn, but ran on the generator for a while.  BTW, Arimas aren't really "butt heavy"........they're actually "Buttlessbuoyant"...........Sorry.....had to make-up a new word to accurately describe it.  :jester:

Yat
History is not the past; it's the present, as we all carry it with us......James Baldwin    
16 SC/Honda 60  (sold)