Hull modifications

[MKP]

Hello Guys,

First post here. I've been looking for some input with a project i am beginning. -Hoping you all have some insight for me.

I have a 32' Roberts ex-bristol bay gill netter. I have converted the interior and top side to a plush sport fishing boat. The vessel has twin 250hp Cummins 6BTAs and is about 20k lbs. WOT is 14.7kts at 2800 rpm with a light load. Wheels are 24 x 18. Shafts are 1.75". She is squirrelly going downhill.

My current priority is to improve economy and speed. Originally the vessel was equipped with skeg keels (one on each shaft) huge 8" x 1/2" steel shoes and 1/2" steel cages around the rudders. You can guess where I am heading with this. I want to reduce drag on the bottom of the boat.

My plan:

Remove both skeg keels
Remove shoes
install longer shafts
remove rudders
install new smaller rudders further aft
increase wheel pitch to fit
add trim tabs - one on each side and one on the centerline
swap wheels for outward turning rotation

I am curious what ideas, experience you guys have offer. Am I moving in the right direction here? Is the work going to be worth the gain? Ideas on trim tab placement?

Thanks in advance,

Mike

[lazeyjack]

First the POS
She has potential to cope with chop, nice fine entry
But my God!!
All that stuff at the stern , and on the bottom, is well agricultural to say the least
yes IMO,you a re on the right track, get rid of it all
You are steel so you have advantages
Once all those early 60, Chevvy finns have gone:))
Put p struts to support the shaft, double up inside with plating to reinforce this area
You have big power and big screws, what is gear ratio
Then can you post rudder sections
This is one neat project, (for some of us) as we don't actually have to do, it, but can sit back and watch you labour away
Now you will have less drag, you will have aboat that does not try steer itself etc, plus you will shed abt 600 lbs useless steel
cheers Stu

[MKP]

Thanks for the reply Stu.

Yes, the boat was a bit overdue for a cleaning. It sat for almost two years during the topside retrofit.

The boat is glass -very heavy glass. Not steel. Some places the glass is near two inches think. The shoes are all made of steel.

Gear Ratio is 2:1

What is a P Strut? I was planning on V struts for extra strength and due to interior access points.

How close should the rudder be to the wheel? Is there a basic rule of thumb here?

What about rudder size? Old rudders were steel plate 22.5"h x 20"d with 1.25" shafts. I'm thinking about a free hanging spade rudder with 1.75" shaft and app 20h x 13.5"d.

[Rick Willoughby]

I can see Stu salivating at the prospect of watching this project develop. I also think it would be entertaining and educational.

I have not done a modification that goes even close to this but I will provide some input for your evaluation.

My estimation of the drag components are as follows:
Wave drag 70%
Transom drag 20%
Frictional drag (clean bum) 10%

I believe the form is one of semi-displacement that will not plane easily. The line of the hull does not promote lift in the mid section where it is needed. Would be interested in your observations here?

By cleaning up underneath there will be a small proportion of the wetted surface removed so a slight reduction in frictional drag. The reduction in weight will likely have a greater beneficial influence by reducing wave drag but the weight reduction is not significant in proportion to the overall weight.

Removing the aft keels may make it more skittish down hill as the stern will slide more readily. May not roll quite as bad because grip is reduced. Personally I think the deep entry is the big contributor to poor control down a wave.

If motor weight is shifted aft it may help handling by lifting the bow but the transom will be deeper and hence increase drag there.

If the underwater is cleaned up with all excess weight removed you might find 0.5kt. Probably about the same as removing the sea life from the hull.

I could be wrong - I have been wrong before. Certainly worth another opinion from someone who has tried something similar. For me I don't think the likely carrot warrants the effort.

Economic speed is likely to around 8kts but the installed power is huge for this speed. Makes me wonder if it was ever repowered.

Rick W.

[TollyWally]

The Roberts hull is a fine boat, well respected. It sounds like you are willing to put quite a bit of effort into this project. A few things to note. Little fishboats like this are designed to be able to take extremely harsh weather conditions and haul weight back to port at adequate speed. They head out filled with ice and fuel, bow down and come back with ice and fish dragging thier asses. The engines are a bit forward to make room for the all important fish hold and to help lever the ass end up under a big load. She probably feels squirrely to you because she rides bow down light.

The skegs and shoes are to help keep the net out of the wheel and let her dry out on the flats. The tunnels allow a bigger more powerful wheel for hard pulling and pushing a full heavy hold full of salmon home that still is protected by the skegs. Those tunnels probably don't help a bit to get her planing.

Others may correct me but I think trim tabs will be more effective in pushing the bow down rather than prying the stern up. As long as you are willing to spend the money and effort a few things come to mind. Shifting the motors back for improved balance, trimming but not removing the skegs, and filling in the tunnels. Possibly moving the tanks. She goes out with full tanks and comes home with lighter ones. The weight of the fuel burned is to partially help balance the boat when the hold fills with fish. Maybe with the weight shifted back towards the stern trim tabs will be effective for tuning the trim angles.

You have a fine boat that is a little bit rough around the edges but well built. The mechanical things that matter will be heavy duty, first rate, hell for stout, and better than yacht grade. Your hydraulic system will make all kinds of things possible and powerful. Boats like yours routinely operate in weather conditions that would absolutely terrorize the vast majority of boat operators in the world.
She is never going to be a speed demon, 15 knots in present trim is respectable. I bet you can do better than 20 optimized. You can do 10 or 12 in rougher conditions than you can imagine and 6 in gale conditions. I wish she was mine! :)

[MKP]

Wow this is some great info. Exactly the input I've been searching for. I have thought about moving the engines aft a few feet. Maybe spinning them around to drive a V-drive.

You are correct, the boat is bow heavy. Even with a load of 400 gallons of fuel and 150 water the stern is a bit high. All tanks are as far aft as possible without infringing on the steering gear. Ideally, where should the center of gravity to be? Aft of midships?

Mr. TollyWally you seem to know Bristol bay boats well. Have you fished up there? Do you know any of Roberts' history. Who were they and where did they go? It is difficult to find info on these boats.

What do you mean by trimming the skeg keels? Maybe trim them to below the shaft log?

Rick, Can you explain to me the difference between wave drag and transom drag? Transom drag is the low pressure caused when the water breaks free of the hull? Wave drag is breaking free from displacement mode to planing?

Thanks again for all your guy's insight.

Mike

[Rick Willoughby]

Mike
All moving hulls experience wave drag. For a hull with low length to beam it is the dominant drag factor between displacement speed and planing speed. So your description is fine.

Transom drag only occurs if the hull has an abrupt cut-off. This creates a low pressure zone behind the stern that contributes to drag. A canoe type stern has close to the same pressure as the bow of the boat as there is no abrupt change. However the canoe stern is wasted on a hull intended to plane.

If you move weight aft to sit the stern down it will add transom drag at lower speed. Interestingly it also will require more power to plane if weight is moved aft.

I agree with TollyWally. It is a fine boat for its intended use.

On the numbers you have provided and pictures it has a lot more installed power than that required for the speed it is achieving if were the ideal shape for full planing. This also supports my view that the hull is really not meant for speeds up around 20kts. It is hard to see the exact shape of the hull where it transitions from the bow to the tunnels but it does not look like a good planing surface.

Rick W.

[MKP]

Shoes are gone. Keels are 1/2 off. Cut to just below the shaft logs. Haven't decided to cut them off completely yet.

Rick here are some more pictures of the hull. Will this thing plane?

[Rick Willoughby]

Shoes are gone. Keels are 1/2 off. Cut to just below the shaft logs. Haven't decided to cut them off completely yet.

Rick here are some more pictures of the hull. Will this thing plane?

It has enough planing surface to plane if the power is up to it.

The things that will not help it plane are the deep forefoot and the prop tunnels. I have not tried to analyse the impact they have but they must be significant at is has ample power to do 20kts if it was a flat run aft with shallow entry. Alternatively you have the weight wrong or the props are underpitched to utilise the power. (The latter could be the case if it is designed for heavy load in heavy weather) I calculate you would need 20" pitch to get 20 kts from 1400rpm at the prop.

It is sometimes sobering to do a weight check if possible. Does the vessel transporter have a load cell? Did they check weight when lifting?

Do the engines rev easily. You said 2800rpm. Is this rated rpm. Do the engines labour in a head wind or she will hold around the 14kts in any condition.

The big props are probably the best set up I have seen short of a tug for the sort of drag required to plane. This of course is a mixed blessing as they have very high efficiency due to the diameter but the tunnel detracts from lift for planing.

I have been in smaller planing hulls with an entry not quite as deep as yours and they are scary coming down a wave. You get caught between backing off to ease into the trough and lose steering or keep powering into the back of the wave and risk broaching.

Rick W.

[MKP]

The travel lifts scale was not working at the time I hauled out.

The engines are rated for 2600. the wheels are under pitched for pushing heavy loads. The engines never labor in any condition. I plan to increase pitch in increments. My prop guy is currently putting a heavy cup on the wheels and I have some 24 x 21 wheels that came with the boat. I want to leave about 100 - 150 rpm spare.

I don't expect this boat to ever do 20 knots. I would like to cruise at a decent 14knots though. I currently cruise 9-10 because it takes twice the fuel to get the extra 4 knots. The boat sort of planes at 14.5 knots but at WOT. I would kill to have the boat cruise on a plane at 14knots at 2100-2200rpm.

Odd as it may seem surfing down larger swells the boat does pretty good. Its the smaller wind chop and steep swells that make for tuff steering. At times it too much for the autopilot.

[Rick Willoughby]

Some drive combinations are actually over pitched to get the engines into the most efficient range at cruise. Trouble with this is that they labour in heavy weather or if pushed hard.

I wonder why it came with spare 21" pitch. These seem more like I would expect for the hull and the installed power.

Altering the pitch can have a small impact on fuel burn but it is hard to escape from the physics that it takes more power to go faster. There can certainly be a point where the drag actually drops away as the boat gets on the plane and you get almost constant power requirement. This is probably around the 14kt mark. The point where the hull levels out.

The viscous drag does become more significant once on the plane so getting rid of the extra area will have increasing benefit as you try to go faster. The numbers certainly suggest you could get to 20kts with the installed power and heavier pitched props.

The tube bundles under the hull probably don't reduce drag either. Fairing block in front and behind them would help providing it does not impair their function.

Rick W.

[Rick Willoughby]

The attached is the Savitsky model approximating your hull. The model that this is based on has cleaner lines though so would likely underestimate. The power shown is for the hull and does not consider prop efficiency and other appendage drag or windage. Typically you could expect about twice the power level shown but you have almost ideal prop diameter so it may not be that bad.

It does show a slight tapering in the rate of increase in drag (thrust) at the start of the curve and levels a bit more over 20kts.

Here is the link if you want to play:
http://illustrations.marin.ntnu.no/hydrodynamics/resistance/planing/index.html

Rick W.

[lazeyjack]

yes you are so lucky Rick has picked up on this one,as I knew he would
I lay thinking abt this in bed, and suddenly those flared bows came to vision, and I thought , WHOOPS not steel, I was so engrossed in the bottom and as I dont know anything abt sticky stuff, will watch, when you get to the eng I can assist more

[MKP]

Wow Rick that graph is a bit over my head. I'm gonna have to digest it a bit more. Very interesting link though. I am learning all sorts of new things about hulls. I ordered The Nature of Boats and the propeller handbook for some added insight. This is really interesting stuff.

I am not sure why the boat originally had 21" wheels. I think it was over propped, but a few sea trails will tell. The previous owner was good friends with a well know diesel guy in Oxnard, CA. I believe they installed the new wheels to get an extra 200 rpm for engine longevity.

The Keel coolers will hopefully be removed in the next few months when the vessel is repowered. I have applied for a grant from the state to install cleaner burning engines. We are planning for QSB 305s which have a bit more hp and a lot more lower end torque which will help my cause.

So my question now is should I trim off the rest of the shaft keels? Or maybe fair in what I have just below the shaft log? You can see the keels are about 8" in diameter and block significant water flow across the wheels. I'm thinking filling in the tunnels will be a tremendous amount of work. The change in shaft angle would have to be so extravagant that it may be counter productive. The angle of the shaft relates heavily to the propellers efficiency correct?

Thanks for the link Rick. I assume that calculator will consume most of my evening.

[Rick Willoughby]

You really do not want to change the prop set up. To have shafts that are near horizontal swinging nice big props is a true blessing. With well selected props you could expect prop efficiency in the high eighties. This is very unusual.

Anything you can do to fair out the appendages can give significant gains relative to unfaired bits. However remember the big drag components come from the stern and general shape at semi-planing speed. Improving the underbody mostly helps the top end when it is on the plane.

Props are now exposed so prone to damage going astern.

The rudder shaft will also need to be able to take bending now. Also I think the "V" strut limited the range of the rudder. This is handy to avoid overloading the steering when going astern. If I am correct here you will need some form of steering stop. Rudder get big forces going astern at any speed.

I would be wary about exposing the shaft any more.

You certainly got stuck into it fast. As Stu said it will be interesting to follow the progress.

Rick W.

[lazeyjack]

you know, props, when a man builds a boat, he picks an engine, then fits a prop to the engine, he should in fact pick a boat, THEN pick a prop then last an engine and ratio to suit the prop

[TollyWally]

I never fished the Bay but I spent 15 years next door in Cook Inlet. A friend of mine had a Roberts 36, the Anna Marie. It was a nice boat. It had a single and did maybe 10 - 12 knots. It is a little bit unusual to see a twin. It is done sometimes, but most guys don't want another wheel to hang up a net in and like the more robust keel with a single. Boats like these are usually custom built to the owners specs. LOL, of course those Bay guys are crazy.

I've never seen one of these with tunnels before. The Bay has big flats, maybe they did it to get in shallower. Normally it would have a keel going all the way back with the shaft and prop exiting at the back of it with a steel plate tying the rudder to it . I realize it is a little too late but I think you are going to want some sort of keel set up on this boat. What I meant by trimming the skegs was cleaning up the net guards and sort of fairing things up.

It's only my opinion but I'm not sure I'd get rid of those keel coolers. I know they cause a bit of drag and don't look very clean but I never heard a guy bitch that they were slowing him down much and they are a really good low maintence way of cooling the motors.

I've spent a lot of time in boats similar to these and really like them. With a single screw and a keel I would feel safe in her up in the Gulf of Alaska in pretty miserable conditions.

I don't know where Roberts were built, probably here in Washington. I can ask around and find out most likely. There weren't a whole lot of them built I don't think but they were well respected boats. I've never heard anyone badmouth them and you certainly can't say that about all of these kinds of boats. The Anna Marie was a nice boat, well built and comfortable at sea.

Maybe I was a little optimistic about 20 knots but once you take the weight of the reel and rigging etc. off and optimise for speed it doesn't seem far fetched. Your v drive idea is interesting. I would have never thought about that. I'll have to ponder it. It might let you fill in those tunnels.

Have you given any consideration to a single screw? It would save considerable weight I think. Some guys like twins for the manueverability and reliability. I've always thought it would be easier and cheaper to keep one motor running reliabily rather than two. Half the filters, fluids, belts, starters, props, shafts, etc. With the hydraulics you already have you can install a damn nice bow thruster for lots cheaper than a motor and get back the manueverability factor. But I'm a single screw kind of guy, you should do what suits you. It is a thought though.

Also did you say what kind of gear you have? Many of these boats have Twin Discs which are Cadillac gears, very heavy duty. You could probably get away with a Velvet drive and save another big chunk of weight.

In any event keep us posted on your project and I really appreciate the pictures. Keep them coming :)

[MKP]

Wally,
Yes the boat has twin disc gears. I wouldn't trade them for the world though. -they're invincible!
I have thought a lot about converting to a single screw, mainly because of the bigger wheel that I can swing. I love the twins though. It handles great and the redundancy in a lifesaver. saved my ass once already when a fuel filter plugged. I drive a tugboat for a living so I am really partial to twin screw boats.

The Keel coolers are awesome but I am repowering to QSB 305s soon and these coolers are not big enough so back to the old heat exchanger I must go.

I think Roberts were made in mount vernon, wa. But I'm not positive.
Where is fox island?

[TollyWally]

I know what you mean about Twin Discs. I was just trying to shave some weight.

LOL, If you're working on a tug you don't need anybody's advice about manuevering boats or what constitutes quality equipment or good practice on a boat.

Mt. Vernon sounds right.

Plug these numbers into a plotter
Fox Island
47.20.315
122.34.624

My boat
47.20.315
122.34.624

Funny you should mention a plugged fuel filter. 3 days back I filled my boat with 100 gallons of newly mandated alcohal enhanced gas and a few miles out plugged my filter. I have twin filters with a valve so I can switch back and forth on the fly. A few miles further filter #2 plugs. Etc. Etc. Etc. Yesterday I swapped out the whole system of primary and secondary filters along with the screens at the carb. There was a rumor that this new fuel could raise havoc. I sure hope it resolves itself with this tank and only a few more filter changes. Having redundant filters makes this a bit less stressful but a motorboat without a motor isn't exactly what I call pleasure boating! Good luck with your project.

[MKP]

I used a load of biodiesel a while back. Lots of crud came floating down river for months. One night coming back in across the bar my port engine died. both the racor 900s and last chance filter was plugged. Made for a tense moment with the wind big swell and ripping ebb tide.

I only run clean reputable #2 now.

[MKP]

i see fox island. Very cool. I grew up in bellevue and had a bunch of friends in vaughn. do you ever go after those big hood canal spot prawns?

[TollyWally]

Every couple years I go after them. The season is so damn short it's not really worth gearing up. It sure was good in the old days though. So do folks in California bitch about people from Washington moving down there? :)

[MKP]

No we only complain about our neighbors to the south.

[TollyWally]

Hey, I had a second thought about your boat. You'll have to run this by some of the more knowledgable guys here but one sort of bullshit hillbilly thing I've seen done on fat heavy bay boats to get them up and planing are adding big aggressive bilge keels, really more like gullwing lifting strakes.

Your boat is by no means a radical example of Bay Boat technology. Long ago the government limited the size of these boats to 32 feet. It was supposed to be a limitation so the natives wouldn't be too outclassed by the Seattle guys. Like all government ideas it didn't work out. The biggest bay boats are over 16' wide and 32 feet long with the nose cut abruptly off. They put 12 cylinder MAN motors in them and then a crew of 3 to 5 spends a short hellish summer chasing salmon in these overpowered abortions. You on the other hand have a fairly nice boat!

[MKP]

The chine on this hull was modified previously. It appears to have been more rounded. Glass over foam was added to create a harder chine and 4" splash rails up forward. The newer glass on this addition holds the only blisters on the boat. The blisters located from the chine up about 8" was odd. I ground out one completely to find foam and under the foam the original bottom.

I am committed to this project now. The keels are coming off completely and with longer shafts and rudders pushed aft.

Does anyone here have experience designing rudders? I am torn between building simple stainless steel plat rudders or ordering a set of bronze buck algonquin rudders. Is there much advantage of the foil shape over plate?

Is there a formulas for figuring rudder size? I am think something about 20 x 13.5...


this boat is once again keeping me up nights...

[TollyWally]

Others might disagree but I've seen plenty fabbed up out of stainless plate. Try this link:www.proboat-digital.com/proboat/200512/?pg=78

[Rick Willoughby]

.....
Does anyone here have experience designing rudders? I am torn between building simple stainless steel plat rudders or ordering a set of bronze buck algonquin rudders. Is there much advantage of the foil shape over plate?

Is there a formulas for figuring rudder size? I am think something about 20 x 13.5...


this boat is once again keeping me up nights...

In terms of the steering force that a particular rudder can generate versus its drag when in line, a foil is substantially better than a rounded nose flat plate.

Taking a NACA0020 profile that is 15" deep and 10" long it will produce a maximum lift coefficient of 0.55. By comparison a flat plate of the same dimensions that is 1/2" thick will have a maximum lift coefficient of 0.23.

Does not look too bad - the foil seems to be only twice as good. Trouble is that is only part of the story where you are draft constrained. Once you start to increase the length of the flat blade the maximum Cd reduces. Lets say the blade is made 30" long but still 15" deep. The maximum Cl is now only 0.1. So although the area has doubled the peak steering force has actually reduced.

The actual situation depends on the available draft but usually a NACA 4-digit foil somewhere between 20 to 25% thickness usually gives close to the optimum result.

If you do not have a skeg to support the rudders then you will need a large shaft to take the bending loads. You need to check the bending but lets say you have a 2.5" shaft. A NACA0020 blade would be 12" long. Go as deep as you can while keeping the blade protected as much as you can by that deep entry. If it ever manages to rise on the plane then the props and rudder could be exposed to damage.

A flat blade will turn you but you are spending a lot of effort to reduce drag. Would be silly to add large flat plates for rudders. It is quite amazing how small the rudder area needs to be if you use a powerful section and keep the aspect ratio (depth/length) up around 1.5 or even higher.

The maximum force on the rudder in full lock at 20kts (say 10m.s) can be calculated as follows:

Force = 1025/2 * 10^2 * Area (sq.m) * Cl.

A NACA0020 rudder 12" long by 20" deep will give maximum force at 20kts of:

Force = 1025/2 *100 * 0.15 * 0.62 = 4766N

This is 1069lbf, say 1/2 ton. With two of them you get a full ton reefing the stern around at about 18 degrees of rudder. This is a lot to handle but then it is related to speed squared so drops off substantially as speed drops. Also it is unlikely you will need full rudder at 20kts.

There will also be a slight increase in water flow in the region of the props but with such large units the flow increase is negligible.

I should add that I do designs for high efficiency pedal powered boats. Here is my latest design in operation near Calgary:
http://www.adventuresofgreg.com/HPB/2008_06_29_archive.html
The rudder on this 24 foot boat is 2" long and 8" deep. It is a NACA0020 and is all that is needed to hold a course and do a circuit.

When I did my early analysis on rudders I looked around for engineering material and found analysis for ships that recommended foils with around 22% thickness for optimum performance.

Rick W.

[MKP]

Rick and Wally,

Thanks this is exactly what I was looking for. Great info! Wally that article from ProBoat was great. Rick, the depth of knowledge you have on the physics behind this is amazing. I must say it is very impressive.

My question for you Rick, is when I determine my rudder shape/size I will most likely match it to an existing production model. How do I know the shaft is of sufficient size? I had 1.25" dia shafts. Most production rudders I have found in my size range have 1.5 - 1.75" dia shafts? Are these sufficient? This boat is built big. Everything is built to receive an extreme punishment. I have kept with this theme with everything I have done, I want do not want to be second guessing my equipment at sea. I would like the rudders to withstand a "hard over" load at full speed with a standard safety factor. How to I insure stock rudder shafts are of sufficient strength?

Your calculations take into effect speed to determine rudder loads, but on a boat like mine wouldn't speed be lower while water velocity over the rudder being relatively high due to greater slip?

Second question is regarding rudder shape inside a tunnel. The previous rudders where close to square. Having the upper area of rudder surface inside the tunnels seems like it might be ineffective and possibly counterproductive, without and easy escape for the water in the tunnel other than in a downward direction when the rudder is at more extreme angles. Would my theory increase drag or effect steering forces in anyway?

[TollyWally]

I can't really comment intelligently but it almost sounds like you are describing a valve. But here is another link from some folks that probably could comment intelligently. If you download the brochures there are some interesting tables etc. that might shed some light on what is stout enough.

Remember the old fisherman's engineering maxim; if it won't bend it won't break :)

http://www.wbmetals.com/

[Rick Willoughby]

A few things regarding the rudders.

You have removed the bottom support on the rudder. The V-strut would provide good support for the bottom. You now have to carry all the load through the top part of the shaft. This means a large bending moment. If you have 20" deep rudders and good foil sections you could generate 1/2T on the blade 10" down.

I know the engineering but I do not know the standards/codes. I am an engineer but boating is only a hobby. My paid work is to prevent insurance losses by looking at ways to design problems out. So i am very conservative.

I would be looking at safety factor of about 3 on bending proniding the shaft is not welded right at the top of the blade. I would go higher if it was welded. If the shaft ends up bigger than 2.5" I would want to look more closely at the detail.

So I support you approach to keep it robust.

As mentioned above these big proips do not slip much so water flow is close to boat speed once you get going.

The blade turning in the tunnel is not quite as bad as you might think. The main issue is loss of efficiency due to having to taper the top back of the blade so it swings without fouling. A blade influences water probably 2 to 3 ft either side of it. Getting rid of the big aft keels will make it more responsive but alos more skittish.

Rick W.

[MKP]

Guys, here is an update on my project.

Absolutely no physical progress to report. The Yard foreman talked me into a speaking with a naval architect before proceeding. His report came today.

The report pretty much confirms my ideas, but has a bit more meat behind the "why?" part.

[Rick Willoughby]

Looks about right. I am certain you did the right thing having it designed properly.

You may nudge the 20kts yet.

I wonder what weight they used for the drag determination. Did you manage to get an actual weight?

You will get gains from bigger engines, bigger props and reduced appendages. Will still take a lot of fuel to push over 14kts. May not have the heavy weather/ heavy load capacity of the current props. Geared more toward speed than workboat.

No doubt you will have at least one interested, if remote, observer in the outcome from the re-commissioning.

Now just a matter of keeping an eye on the workmanship. Prop strut and rudder mounts will be heavily loaded points.

Rick W.

[MKP]

Rick,

I never did get a good weight. The naval architect used 7.5LT. I am guessing he took some measurements and made a crude estimate of the block coefficient and determined the displacement. I actually asked the same question today. I'll let you know his response.

I'm not too worried about losing the load capacity of the current props. The boat will never again carry the loads it was intended to, as she is now a light commercial and sport fishing charter vessel. Speed and economy are my current priorities.

A lot of people think i am crazy for making this modification. I do believe the increase of 6 knots is worth the trouble. Hopefully the boat will be more efficient and justifying the cost of the improvements. Fuel savings may not be realized for many years.

Now the big question...who specializes in refinancing poor boat owners through ridiculous yard periods??

[Rick Willoughby]

Would have been good to get a starting weight. Even a good photo of where she sat in the water before any mods. Getting weight out is one certain way to save fuel.

I am trying to fund my own little projects while building my retirements funds but just treading water with the sharemarket is doing its best to make me poor. So I am not in a position to help.

Best of luck with the funding. I do hope you get up around the 20kts. Keep us posted on progress.

Rick

[TollyWally]

Hey MKP,
Good to see you and your project back. Sounds like you're going ahead full steam. It's a shame the travel lift at the yard you're laid up in doesn't have a strain gauge to get a weight. I'm trying to sweet talk the local guys to make a quick 1 minute pick and drop to get an accurate weight for my boat and my records.

The yard I do my regular haulouts at has to use a carriage and a ways before they can pick with a travel lift. Much more hassle and time involved. I am quite annoyed with myself for not getting a weight reading last time I hauled. All I had to do was ask!

Keep us posted, I am quite interested in your project.

[MKP]

Finally got a solid week of work in from the yard. Things are going slow, but at least moving in the right direction. Rudders and steering gear ordered today. I found a guy at Yacht Supply Depot that has great prices if anyone needs Buck Algonquin parts.

5 days rough days and the shaft keels are completely gone. Only a small piece is left to hold the cutlass bearing.

I think I am going to spend the extra money for Aquamet 22 Shafts instead of AQ 19.

Do you guys have a shaft material preference?

Next week the glass work begins and hopefully some rudder hanging.

Pictures from the week:

[MKP]

Hey Guys. I finally got the boat back in the water!

Here is the official report (performance specs to follow):

On June 12th I hauled her out for a bottom job and a quick evaluation by a Naval Architect. Well...one thing turned into another and now, four months later, she is back.

I have been toying with ideas to make her faster and more efficient. She originally had triple keels. One center-line and one for each shaft. The shaft keels had huge steel shoes and cages around the running gear. This was for working in the shallow waters of Bristol bay and jumping gillnets. -none of which is required locally. All this extra gear was added weight and drag.

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1566.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1582-1.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1576.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1596-1.jpg

In addition to a bottom job and a hull polish, I planned to reduce as much as possible drag on the boats bottom, relocate the wheels and rudders to make her a little more streamlined. The naval architect's report confirmed my theory. So one afternoon I armed myself with a case Coors, two dozen sawzall blades, and a Tyvek suit and got busy.

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1622.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1640.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1769.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1784.jpg

Basically everything that wasn't hydrodynamic or absolutely necessary was removed.

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1831.jpg

The new free hanging spade rudders were moved aft for a greater steering moment. The new foil rudders replaced old flat plate skeg rudders and should be 30% more efficient.

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1844.jpg

Shafts were enlarged and extended to move the wheels aft by 2' to throw a larger wheel. With the removal of shaft keels, nothing was in place to hold a bearing, so two struts were fabricated and a second cutlass bearing was placed at the new shaft log location.

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1845.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1846.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1866.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1875.jpg

Numerous other related projects were accomplished during this time. You know how it goes: "well while we've already got that open, so we might as well..."

In hine sight the project was far more expensive and longer than I ever expected. This was not a financially smart endeavor. I do not know the exact fuel savings yet, but I can predict it will take many many years to offset the cost of this modification. I'm more of an Ops guy than a bean counter!

Finishing touches:
http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1870.jpg

New Interceptor Trim Tabs:
http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1919.jpg

Back in the water:
http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1933.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1925.jpg

More pictures here:http://s47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/

[Rick Willoughby]

That looks like 4 months of satisfaction. Looks much "cleaner" underwater now. I said at the beginning it was a brave move and would be hard to justify economically but it does look nice now. I believe you got some good input on the detail design it looks robust.

So did you get to 20 knots?

Did you get a weight when relaunching?

What size are the props? They look nice by the way. They are monsters compared with most.

Any estimate of fuel saving yet?

Is she more responsive now? Not skittish down a wave?

Rick W.

[MKP]

Seatrails are planned for tomorrow. Still finishing up some steering issues.

Weight on the travel lift was 15k lbs close, but seems a little lite to me.

I moved up from 24 x 18 to 24 x 21. Sounded like a good place to start. The boat has room for 28".

I will report tomorrow night on the performance specs.

Thanks for all your input!

Mike

[TollyWally]

Congratulations!

You've accomplished a great deal. I am extremely interested in the results of your trials. Now the hard part...dialing it in. Once again, congratulations!

TollyWally

[MKP]

I'm worried the rudders aren't big enough.

Here are some interior pictures of the new rudder Assembly. I turned the tillers facing aft for more work/storage room:

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1911.jpg

http://i47.photobucket.com/albums/f193/mkp77/Blizzard%2008%20Retrofit/IMG_1912.jpg

[MKP]

Finally got some time to write up the seatrial data. -See attached

At WOT I saw 19.2 knots with a marginal load. Engines are rated for 2600 rpm at full load, but I am still seeing 2840. Governor is set at 3030.
I may still pitch up a few inches.

Tachs are off a bit, but equally between the two engines.

[Rick Willoughby]

Great data to have for future reference. I will have to see how it compares with estimates.

Almost where you wanted to be. Will be interesting if a bigger pitch will make it to 20kts.

One other thing I thought about from your photos. The one showing the rudder shaft support. It does not seem that there is good transverse restraint of the upper bearing. The prop is producing a side load so the bearing needs good transverse restraint. It may have it but there is no transverse web visible in the photo.

Rick W.

[Rick Willoughby]

From 14.7 to 19.2 kts is a big gain. I wonder if you will save fuel?

Looks like your previous top speed will now be the economic cruise speed. From the charts that should be 1nmpg at 14kts. I cannot recall if you posted a figure previously.

Rick W

[Rick Willoughby]

The travel lifts scale was not working at the time I hauled out.

The engines are rated for 2600. the wheels are under pitched for pushing heavy loads. The engines never labor in any condition. I plan to increase pitch in increments. My prop guy is currently putting a heavy cup on the wheels and I have some 24 x 21 wheels that came with the boat. I want to leave about 100 - 150 rpm spare.

I don't expect this boat to ever do 20 knots. I would like to cruise at a decent 14knots though. I currently cruise 9-10 because it takes twice the fuel to get the extra 4 knots. The boat sort of planes at 14.5 knots but at WOT. I would kill to have the boat cruise on a plane at 14knots at 2100-2200rpm.

Odd as it may seem surfing down larger swells the boat does pretty good. Its the smaller wind chop and steep swells that make for tuff steering. At times it too much for the autopilot.

Mark
I just went back through the posts. Hope you did not need to kill anyone!!!

Seems like it is close to where you wanted to be.

The one other thing that you were after was better handling downhill. Do the new rudders achieve this?

Rick W

[MKP]

Nope, I did not have to kill anyone. Just paid handsomely for it.

We did not expect the gains that we got. I am VERY happy with the results. I do not have specific fuel consumption data prior to the modification, but I am sure I am much more efficient now.

We fabricated a support for the upper rudder shaft bearing with fiberglass over 3/4" marine ply. The platform is glassed to the transom as well as each stringer. I have plans to stiffen it up a bit with some supports on the foward end. I've put it through full-ahead and hard-over maneuvers and it has all held well.

The downhill handling is about the same. When in a large seaway on the quarter the boat tends to veer towards the same side as the swell. I believe this to be related to the fine entry of the bow. The new rudders which were moved further aft are much more efficient at handling the boat in this condition. So to answer your question. Yes the handling is better. There is more rudder response. However the boat is still a handful in a larger following sea. Sometimes to the point where the autopilot will not hold a course. -but all still better than previous setup.

New engines will be ordered within the next few weeks. QSB 305s paired with ZF tranny will be installed this winter adding 100 hp to the scenario. Might see upwards of 24kts now.

[MKP]

You can sort of see the new bearing support is glassed to an previous platform that is glass to about 4 feet of transom. should be plenty of transverse support.

[Rick Willoughby]

The glassing to the transom solves the transverse restraint. I could not see that important detail.

Looking at your speed versus rpm there is a lot of power to get from 6 to 10kts so I guess things start to settle out after 10kts. Fuel consumption (nmpg) is almost constant from about 10 to 15kts so your target cruise speed of 15kts should be economic.

Rick W

[MKP]

14-15kts seems to be the sweet spot.

Now I need to put some insulation in! I'm now running at high rpms and the noise is fatiguing.

Any suggestions on sound absorbing material?

[Rick Willoughby]

14-15kts seems to be the sweet spot.

Now I need to put some insulation in! I'm now running at high rpms and the noise is fatiguing.

Any suggestions on sound absorbing material?

I have not actually directly purchased soundproofing materials but I have had experience with soundproof generator enclosures. The stuff I have seen I believe is dense glass fibre with a perforated aluminium sheet to hold it in place. I have attached a photo of what I mean but I could not find a reference for this. It is very effective and the aluminium is heavy enough that it does not dent if it gets handled.

Here are a few sites I found while looking for the aluminium faced stuff:
http://www.soundprooffoam.com/raf-melamine-foam.html

http://www.marinefoam.com/marine-grade-ultra-barrier-plus.html?page_type=engine-soundproofing&link_type=image

http://www.noisestopsystems.co.uk/Soundproofing_solutions/Soundproofing_material.asp

As far as foam goes I would be very careful about the fire rating. I would want to understand more about the UL or FM classifications regarding flammability. Some foam has fire retardants and will not burn with a naked flame but they will produce fume under high temperature and this will explode if it gets to the right conditions.

I am sure there are others here who have first hand experience with sound proofing.

Rick W

[petergt]

Hi MKP,
Without doing detailed noise measurement and analysing the frequency of the noise in the boat, it is difficult to be 100% certain what the source of the noise is.
My guess would be most likely due to the 5% blade clearance causing blade pass vibration and consequent noise, which is a common problem with high speed boats and with low prop clearance. This can be difficult to get rid of (particulary given the high amount of energy forcing the vibration and noise). If you imagine the high amount force generated by a single propeller blade passing the bottom of the hull



Options to fix include
1) Increase the blade clearance (assume this is not a good option for you)
2) Try to see if the flow into and above the prop can be improved,as this can increase the problem. It is not so easy to see from the photo, but the struts look to be fairly blunt, that could cause more turbulent flow into the propellers and hence increased noise and vibration.
Poor tunnel entry (or separation in the tunnel) can also affect this, but your tunnels appear to be fairly long
3) I am assuming the struts are fairly rigidly mounted, but this should be checked

It is best to fix the problem before it gets into the hull as once in the hull it can travel as structure borne vibration to other parts of the boat, and pop out as more noise.

Putting your hand on the hull near the prop can sometime provide an indication as to where major vibration areas are occuring, but this is pretty rough. To provide a proper analysis however a noise consultant can bring a noise and vibration meter to tell you what the source of the problem is suggest what should be done to improve this (preferably one that knows what a boat is - Local shipyards may know people who can do this). Although there are no guarantees here, this is a better approach as sometimes you can tackle areas that are not the source of the problem and waste your money.
The other possibility is to find local companies experienced in supplying noise materials for boats and get their advice (cheaper, but may not adress the source of the problem).
It can get complicated and they can give you an idea of the materials that can be used to help solve the problem. Get good advice from experienced people as noise fixes tend to have a high failure rate for various reasons. Ask for references and speak to the boats owners to see if their past noise fixes worked.

Once into the hull there are 3 main types of noise materials utilised

1) Noise insulation - Like noise foam. Good and absorbing airborne noise, but may be of limited use for blade pass problems
2) Noise barriers - 5kg/sqm vinyl sheet is one type and reduce a certain amount of airborne noise travelling through them ie may be 100 dbA on one side of BHD and 80DbA on the other hence 20 dBA attenuation. The heavier barrier the better. Concrete is a great noise barrier and hence often used in buildings to stop noise. This are OK on high speed boats, but given the weight aspect they are used in limited quantities. Any hole in a noise barrier will short circuit the barrier, significantly the effect of the barrier
3) Noise dampeners - Often fixed/glued directly onto structure to reduce structure borne noise. Thickness of this varies with structural thickness of the member (often in car panel to quieten cars)

Often to fix to noise problem varying combinations of the above 3 will be used. The best solution is to minimise the amount getting into the structure as it more expensive to remove once it becomes structure borne vibration

Hope this helps

[MKP]

Wow Thanks guys! That was a lot of info. Most of my noise is engine related now. Before the modifications I had a ton of vibration and noise from the wheels, but now I currently have 18% prop clearance and the noise is minimal.

The turbo's are the single most apparent offender.

I like the aluminum and glass down deadening material however, I believe I do not have the space in the engine room to maneuver panels into place.

Does anyone have experience with the foam, lead, aluminum foil material? Is it flame-retardant?

[DBM]

I suggest you use pick-up truck bed liner spray. THis works especially well on sheet metal. Fill up any gaps and through bulkhead holes and spaces first with fire resistant expanding foam. New rubber seals on all hatches and doors really makes a difference too.