boat bottom width?

no excuses

I've posted enough I should edit this section
Jun 11, 2012
261
78
52
Oregon/USA
Name
Stan
Boat
sea-doo fish pro
Looking at building a boat in the next year and had a question about bottom width. Looking at a few plans from specmar. Looking at going with 30' length and at least 10' width. Boat will be a true walk around pilot house 6'-6.5' wide and 8'-9' long. The deadrise is in the 20-21 degree range.
How much difference will going from a 8.5' wide bottom to say a 9'-9.5' bottom have on ride, fuel economy and stability at rest?

Couple of the specmar plans I am looking at (still early stages) are the

which would be streched to 30', cabin changed to pilot house and 250gallons of fuel. This boat has a 10' beam and a 9'4" bottom width

the deck would be raised to level and cabin again changed to walk around. This boat has a 10'9" beam and a 8.'6" bottom
 

Pacific Jigger

You’ll never know unless you go
Sep 16, 2019
342
484
45
United States
Name
Bud
Boat
Formula 233
I’ve been down the road you’re traveling. Specmar has some good designs.
If you’re going to go to the effort and expense of building, you really should see what Conrad Yacht Designs up in B.C. has in their portfolio. Far more advanced and interesting than Specmar. A number of his hulls are in operation and they’ll really perform.
 

Uncle Binky

Proficient at swapping lower units
Oct 17, 2010
540
334
Monroe WA USA
Name
Mark
Boat
Herring Voices - Grady White 265 Express
Beam is king. The difference isn't just noticeable, it makes every aspect of boating and fishing better. I'll take a foot of width over 2 feet of length any day. I strongly advise that you get out on the boat you plan to build before committing to marrying a girl you've never met.
 

af dreamer

I've posted enough I should edit this section
Apr 16, 2007
4,526
2,147
long beach,ca
Name
tom
Boat
44 luhrs dreamer
Bertram did some tests years ago,on bigger boats but interesting.They took like a 50 hull and stretched it and it gain speed,they did the same hull but made it wider but not longer and it lost speed.FWIW,Tom
 

KimH

Someday I'll live the dream.
Mar 4, 2009
2,536
2,258
Tacoma/Westport WA/USA
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Kim
Boat
26' Duckworth..."Mayhem"
Bertram did some tests years ago,on bigger boats but interesting.They took like a 50 hull and stretched it and it gain speed,they did the same hull but made it wider but not longer and it lost speed.FWIW,Tom
I think to a certain point that’s been a rule of thumb. Gain speed with some length.
 
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G-Spot

Captain
Mar 14, 2008
4,912
2,071
Salem/OR/USA
Name
John
Boat
53’ Hatteras STEEL N TIME
Bertram did some tests years ago,on bigger boats but interesting.They took like a 50 hull and stretched it and it gain speed,they did the same hull but made it wider but not longer and it lost speed.FWIW,Tom
It can be very true depending on many factors.

My boat partner and I have a 53’ Hatteras. A guy we know has a 60’ Hatteras, with same engines, and a little more weight. His boat gets 20% more hull speed at low rpms. He also get better fuel economy at his hull speed.
 

no excuses

I've posted enough I should edit this section
Jun 11, 2012
261
78
52
Oregon/USA
Name
Stan
Boat
sea-doo fish pro
I’ve been down the road you’re traveling. Specmar has some good designs.
If you’re going to go to the effort and expense of building, you really should see what Conrad Yacht Designs up in B.C. has in their portfolio. Far more advanced and interesting than Specmar. A number of his hulls are in operation and they’ll really perform.
I will check them out, thanks.
 

no excuses

I've posted enough I should edit this section
Jun 11, 2012
261
78
52
Oregon/USA
Name
Stan
Boat
sea-doo fish pro
Beam is king. The difference isn't just noticeable, it makes every aspect of boating and fishing better. I'll take a foot of width over 2 feet of length any day. I strongly advise that you get out on the boat you plan to build before committing to marrying a girl you've never met.
I plan on getting out on the boats on my short list before I commit. I agree, wider is better on the beam.
 

no excuses

I've posted enough I should edit this section
Jun 11, 2012
261
78
52
Oregon/USA
Name
Stan
Boat
sea-doo fish pro
Bertram did some tests years ago,on bigger boats but interesting.They took like a 50 hull and stretched it and it gain speed,they did the same hull but made it wider but not longer and it lost speed.FWIW,Tom
So maybe the wider beam and narrower bottom would be more efficient.
 

Pacific Jigger

You’ll never know unless you go
Sep 16, 2019
342
484
45
United States
Name
Bud
Boat
Formula 233
Wider beam and narrower bottom, i.e, more slope to to the sides and more weight above waterline, makes a boat less stable when drifting or underway at hull speed.
Length vs width is a choice only you can make for your purposes and it simply comes down to stability and room vs economy.
Building jet boats, we’d build as wide as possible for any given length because it lowered the planing speed, which gave more time to analyze the water ahead when running and lowered the speed you’d have to run to stay on step when cornering tight. It also took more power to plane but the trade off was worth it in that application.
 

no excuses

I've posted enough I should edit this section
Jun 11, 2012
261
78
52
Oregon/USA
Name
Stan
Boat
sea-doo fish pro
I had a 24' NR seahawk with a 8.5' beam and 7' bottom, 18 degree hull and it was way more stable then the 27 (actually 30')contender open that I had later with the 24 degree hull. The contender of course rode better(deeper V, longer and heavier) but it rocked and rolled a lot on the drift. Could not use cooler as they were dangerous rocking from side to side.
 

Pacific Jigger

You’ll never know unless you go
Sep 16, 2019
342
484
45
United States
Name
Bud
Boat
Formula 233
That comes back to hull shape and degree of vee. The lighter shallower vee aluminum hull is going to win the stability at rest contest every time. My brother owns a 21’ NR Seahawk and I currently own a completely rebuilt Formula 233, which is a 24 degree hull. The key on the deep v hulls is weight low in the belly. I have dual 100 gallon fuel tanks as low as possible right on the center line and it really helps. It’s still not as stable as the Seahawk but oh so much nicer running hard and headed west.
 

no excuses

I've posted enough I should edit this section
Jun 11, 2012
261
78
52
Oregon/USA
Name
Stan
Boat
sea-doo fish pro
That comes back to hull shape and degree of vee. The lighter shallower vee aluminum hull is going to win the stability at rest contest every time. My brother owns a 21’ NR Seahawk and I currently own a completely rebuilt Formula 233, which is a 24 degree hull. The key on the deep v hulls is weight low in the belly. I have dual 100 gallon fuel tanks as low as possible right on the center line and it really helps. It’s still not as stable as the Seahawk but oh so much nicer running hard and headed west.
the contender is based off the Formula 233 hull, it held 210 gallons of fuel, 110 in the center and twin 50's on the outsides but all in the hull. First trip out with it we were drifting on a tuna bait stop and the coolers were sliding back and forth from side to side. Smashed a buddies foot and ankle we thought it broke it for a few. I went with kill bags after that as they did not slide.
 

Uncle Binky

Proficient at swapping lower units
Oct 17, 2010
540
334
Monroe WA USA
Name
Mark
Boat
Herring Voices - Grady White 265 Express
First trip out with it we were drifting on a tuna bait stop and the coolers were sliding back and forth from side to side. Smashed a buddies foot and ankle we thought it broke it for a few. I went with kill bags after that as they did not slide.
We have a hard, fast rule about loose coolers on the deck. They stay in the truck back at port. A couple of kill bags on the bow for when the fish boxes are full. I'd rather chop heads and stuff the fish boxes than take up the room we are all agreeing is so important. My 55 gallon bleed barrel takes up enough room as it is, but I won't go out without it.
 

G-Spot

Captain
Mar 14, 2008
4,912
2,071
Salem/OR/USA
Name
John
Boat
53’ Hatteras STEEL N TIME
So maybe the wider beam and narrower bottom would be more efficient.
You don’t build a custom boat and spend a shit load of money for efficiency... Too narrow and you will roll back and forth on a drift... You need to find a balance and give up a little “efficiency” for the right boat.

Design, width, weight up high, sharpness of V..... all important... Don’t focus on any one component like efficiency as a goal.... Find a balance on each item, and the efficiency will have to be what it is....
 
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Hard Chargin'

Fischjäger
Aug 11, 2019
495
308
31
PNW
Name
Andre
Boat
Stabicraft 459 Fish'r
A crusty old engineer friend of mine once told me "Andre, every project you work on is a collection of compromises. You just hope you made the right I ones." Same is true here. Efficiency, affordability, seaworthiness, stability, speed, durability, weight. You cant have the best of all if them.

Now I don't know a lot. And I knew even less a year ago, but I was recommended several great books on boat building by members here and I have done many many dozens of hours of continued research on the subject.

I would recommend:

Large hard chines- this will help keep your ride dry, increase efficiency, and most importantly increase stability at rest. The downside is that they will slap in a chop and I believe reduce your top end a touch.

Beam- at the top as well as the bottom. Sloping sides will increase your propensity to a lot of roll. I would want the sides almost straight up and down at the transom.

Freeboard- longer gaffs and nets are cheap.

Now just to throw some wrenches in it. If I were getting a boat built I would absolutely do inboard diesel. That's a different discussion entirely but if you're building from the ground up I would seriously consider it. A 2" shaft spinning a 24" wheel rarely let's anyone down.
 

Hard Chargin'

Fischjäger
Aug 11, 2019
495
308
31
PNW
Name
Andre
Boat
Stabicraft 459 Fish'r
I have no idea how I put the line through my last sentence... And I have no idea how to take it out haha.
 
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TJM

Newbie
Oct 17, 2018
2
0
36
SW Washington
Name
Trevor
Boat
Too Small
I have the 27' sportfish you are looking at. It was modified to 23 degrees deadrise with a delta pad added. 260 gallon fuel capacity. You will appreciate the additional bottom width for stability at rest.
 

Walker Inc.

I've posted enough I should edit this section
Jun 24, 2013
2,944
6,754
Gig Harbor, WA
Name
Patrick Walker
Boat
33 ft. Coldwater Walkaround
Looking at building a boat in the next year and had a question about bottom width. Looking at a few plans from specmar. Looking at going with 30' length and at least 10' width. Boat will be a true walk around pilot house 6'-6.5' wide and 8'-9' long. The deadrise is in the 20-21 degree range.
How much difference will going from a 8.5' wide bottom to say a 9'-9.5' bottom have on ride, fuel economy and stability at rest?

Couple of the specmar plans I am looking at (still early stages) are the

which would be streched to 30', cabin changed to pilot house and 250gallons of fuel. This boat has a 10' beam and a 9'4" bottom width

the deck would be raised to level and cabin again changed to walk around. This boat has a 10'9" beam and a 8.'6" bottom
It’s all about girth. The wider the better. Most woman will agree!!!

mine is 10’10”. No tapered sides. Big hard chines. .90 MPG on a nice ocean, .70 MPG in a shitty ocean. Stability at rest, priceless.

492666F7-2E82-40D1-A6BB-F5DEDF7C1E65.jpeg
 

G-Spot

Captain
Mar 14, 2008
4,912
2,071
Salem/OR/USA
Name
John
Boat
53’ Hatteras STEEL N TIME
It’s all about girth. The wider the better. Most woman will agree!!!

mine is 10’10”. No tapered sides. Big hard chines. .90 MPG on a nice ocean, .70 MPG in a shitty ocean. Stability at rest, priceless.

View attachment 1206008
Hey.... Not sure if you noticed..... Your missing something... 🤔
 
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