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Naval Architect need

BA
Bob Austin
Sun, Aug 15, 2010 2:09 AM

A few comments:  Some of the most common mistakes made by amateur boat
builders are: modifying the plans, and making the boat too heavy.

My boat was not the  standard
design. It had a 15' beam to satisfy the NC DOT for highway transport.  It
was built to "T" boat standard which necessitated increasing the hull
thickness....but the equivalent US measure plates are slightly  thicker.

The design beam was 20 feet, and it was decreased by 5 feet or 25%--a large
amount;  we don't know exactly how the lines were changed, but the
assumption is that the NA OKed any changes, and re-did the calculations.
The increased plate thickness and perhaps all of the scantlings were
increased by the more rigid specs.  All of this added to increased weight.

My boat holds 1800 gallons of fuel outboard of the engine room.....will

not hold enough fuel to cross oceans.

There are any number of similar sized vessels which have small engines and
relitatively small fuel capacities.  I had a similar sized motor sailor and
at 6 knots would only burn a gallon an hour, with 85 hp. With 500 gallons, I
had over 2700 miles of range. (Granted that the lines were finer than the
Spray).  One does not have to go 8 to 10 knots when crossing oceans--and if
you look at Voyaging under power, there any many vessels which are capable
of transoceanic voyages with moderate amounts of fuel.
The 1800 gallons of fuel is a very large amount for a 52 foot boat for
coastal cruising, and there is some "risk" in keeping large amounts of fuel
which is not regularly re-circulated or used and replaced, for contamination
with water and algae (and byproducts).  So if you have several tanks on each
side, you can only carry fuel in the most forward of the tanks, and fill up
a bit more often--as you use the fuel.  1800 gallons should certainly be
enough to cross any of the several power circumnavigation routes.  Lets say
that you get only 2 miles a gallon: that gives you 3600 miles (no
reserve)--or at 1.5 miles a gallon, 2700 miles--enough for most passages.
For example looking at Voyaging Under power; Seaton's "Sluggo" is 52' 9"
LOA, 48'3" LWL , 17'4" and 6' 2" draft  (Disp 81,000 lbs).  With 195 HP and
fuel capacity of 1925 gallons estimated range at 8 knots of 3077 miles--if
if dropped down to 7 knots, that range shoots up to over 5500 NM! Taking a
larger and much heavier Seaton Design 256, 59' 9" LOA, 19' 6" Beam, 9' draft
and 226,000 lbs displacement, will still have a range of over 3000 miles if
dropped down to 6 knots with this same 1800 gallons of fuel.

If I add all the ballast it  will  have a uniform excessive deep draft.
The specification called for a 2/3
loaded draft of 6 feet. My expectation is that the loaded draft aft will
be
closer to 8', submerging the rubrail and wet exhausts. SO the boat is not
practical to use inland with a 7' draft...

I must differ--having cruised the Med, Baltic, all of the Coast of North
America (including Atlantic ICW and Gulf ICW), Caribbean and S. Pacific,
with 7 feet draft--this is not at all prohibitive.  It means that you do
have to do more planning--be careful about marinas, and perhaps anchor out
more--and occasionally go "outside".  But there are few places that will be
off limits--and you can even cruise much of the Bahamas with this draft.
The majority of inland waterways and rivers will be accessible to a boat
with 7 foot draft.

.>    Hopefully there is a fix by adding buoyancy to the  stern. We'll
see.....

There is a quick and dirty way to see what the effect of adding buoyancy to
a vessel.  I noted this "trick" which is used by a steel boat builder who
occasionally launches vessel with greater draft than our local waterway
allows.  He straps large blocks of Styrofoam under the aft buttocks of the
vessel, and uses these as "floats" to temporally decrease the draft.  You
can shape Styrofoam floats, strapped under the stern quarters to see what
the effect of modifications would be--you can even operate the boat at slow
speeds with this to see what change in handling there is.    It has been not
uncommon to add bustles to racing sailboats--mostly for rule changes--but
sometimes for performance.  So you can modify the aft sections--but this is
expensive, potentially fraught with some risks--it must be well designed.
You may want to put in a smaller engine, or even move the fuel tanks.  Also
you may want to think and calculate carefully where extra ballast is placed.
If there is more weight in the ends, a vessel is more likely to "hobby
horse" in seas, and in general there will be adverse affects in performance.

I understand that there is a high level of frustration after a lot of blood,
sweat and expense.  But there are a number of options which will allow you
fulfill  your dreams.

Bob Austin

A few comments: Some of the most common mistakes made by amateur boat builders are: modifying the plans, and making the boat too heavy. > My boat was not the standard > design. It had a 15' beam to satisfy the NC DOT for highway transport. It > was built to "T" boat standard which necessitated increasing the hull > thickness....but the equivalent US measure plates are slightly thicker. The design beam was 20 feet, and it was decreased by 5 feet or 25%--a large amount; we don't know exactly how the lines were changed, but the assumption is that the NA OKed any changes, and re-did the calculations. The increased plate thickness and perhaps all of the scantlings were increased by the more rigid specs. All of this added to increased weight. >My boat holds 1800 gallons of fuel outboard of the engine room.....will not hold enough fuel to cross oceans. There are any number of similar sized vessels which have small engines and relitatively small fuel capacities. I had a similar sized motor sailor and at 6 knots would only burn a gallon an hour, with 85 hp. With 500 gallons, I had over 2700 miles of range. (Granted that the lines were finer than the Spray). One does not have to go 8 to 10 knots when crossing oceans--and if you look at Voyaging under power, there any many vessels which are capable of transoceanic voyages with moderate amounts of fuel. The 1800 gallons of fuel is a very large amount for a 52 foot boat for coastal cruising, and there is some "risk" in keeping large amounts of fuel which is not regularly re-circulated or used and replaced, for contamination with water and algae (and byproducts). So if you have several tanks on each side, you can only carry fuel in the most forward of the tanks, and fill up a bit more often--as you use the fuel. 1800 gallons should certainly be enough to cross any of the several power circumnavigation routes. Lets say that you get only 2 miles a gallon: that gives you 3600 miles (no reserve)--or at 1.5 miles a gallon, 2700 miles--enough for most passages. For example looking at Voyaging Under power; Seaton's "Sluggo" is 52' 9" LOA, 48'3" LWL , 17'4" and 6' 2" draft (Disp 81,000 lbs). With 195 HP and fuel capacity of 1925 gallons estimated range at 8 knots of 3077 miles--if if dropped down to 7 knots, that range shoots up to over 5500 NM! Taking a larger and much heavier Seaton Design 256, 59' 9" LOA, 19' 6" Beam, 9' draft and 226,000 lbs displacement, will still have a range of over 3000 miles if dropped down to 6 knots with this same 1800 gallons of fuel. > If I add all the ballast it will have a uniform excessive deep draft. > The specification called for a 2/3 > loaded draft of 6 feet. My expectation is that the loaded draft aft will > be > closer to 8', submerging the rubrail and wet exhausts. SO the boat is not > practical to use inland with a 7' draft... I must differ--having cruised the Med, Baltic, all of the Coast of North America (including Atlantic ICW and Gulf ICW), Caribbean and S. Pacific, with 7 feet draft--this is not at all prohibitive. It means that you do have to do more planning--be careful about marinas, and perhaps anchor out more--and occasionally go "outside". But there are few places that will be off limits--and you can even cruise much of the Bahamas with this draft. The majority of inland waterways and rivers will be accessible to a boat with 7 foot draft. .> Hopefully there is a fix by adding buoyancy to the stern. We'll see..... There is a quick and dirty way to see what the effect of adding buoyancy to a vessel. I noted this "trick" which is used by a steel boat builder who occasionally launches vessel with greater draft than our local waterway allows. He straps large blocks of Styrofoam under the aft buttocks of the vessel, and uses these as "floats" to temporally decrease the draft. You can shape Styrofoam floats, strapped under the stern quarters to see what the effect of modifications would be--you can even operate the boat at slow speeds with this to see what change in handling there is. It has been not uncommon to add bustles to racing sailboats--mostly for rule changes--but sometimes for performance. So you can modify the aft sections--but this is expensive, potentially fraught with some risks--it must be well designed. You may want to put in a smaller engine, or even move the fuel tanks. Also you may want to think and calculate carefully where extra ballast is placed. If there is more weight in the ends, a vessel is more likely to "hobby horse" in seas, and in general there will be adverse affects in performance. I understand that there is a high level of frustration after a lot of blood, sweat and expense. But there are a number of options which will allow you fulfill your dreams. Bob Austin