V-Hull Diesel

Now why don't I want to run a V Hull at Hull speed. They seem more affordable and a lot less Rolly.

Wzdr02 said:

Now why don't I want to run a V Hull at Hull speed. They seem more affordable and a lot less Rolly.

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I have a Bayliner Victoria 2750 Command Bridge I recently repowered with a 50 hp Perkins 4.108 Diesel. She has a vee hull. I run at hull speed or less. In fact, the boat is not capable of going over 7 knots. In protected waters, it is stable. In swells above 3 feet, it is very rolly at hull speed. I keep and run her in protected waters and she does extremely well and sips fuel.

You can absolutely run a vee hull at hull speed. It will not be quite as efficient as one designed for that speed, but it will not be terrible at all.

The purpose of the V hull is to be able to smash into waves at high speeds and lower the G loads on the occupants.

Otherwise its just more surface area to drag thru the water.

Like an immersed transom the difference in fuel burn might be 10% 15% worse , but at 1.5 GPH , who could notice?

V Hull

My thinking is to buy a 36 to 44 foot liveaboard V hull if I can't find a trawler I want. We intend do do this every winter from Florida to the islands. What is the draw back other than a little fuel economy more wear on the engines BUT you can go fast if you need to.

Wzdr02 said:

Now why don't I want to run a V Hull at Hull speed. They seem more affordable and a lot less Rolly.

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Ski in NC said:

You can absolutely run a vee hull at hull speed. It will not be quite as efficient as one designed for that speed, but it will not be terrible at all.

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FF said:

Like an immersed transom the difference in fuel burn might be 10% 15% worse , but at 1.5 GPH , who could notice?

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You can. We do, often. What Ski and FF said.

The ride can sometimes be a lot MORE roll-y depending on sea states and wave direction relative to travel... compared to a hull with a real keel, even more so if compared to a stabilized boat. In these cases, we usually just get on plane. And/or tack.

You might want to read threads about keeping your diesels at appropriate operating temperatures, periodic "cruise" RPMs and even occasional WOT.

-Chris

ranger42c said:

The ride can sometimes be a lot MORE roll-y depending on sea states and wave direction relative to travel... compared to a hull with a real keel, even more so if compared to a stabilized boat. In these cases, we usually just get on plane. And/or tack.
-Chris

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At displacement speeds a V hull acts much like a round bottom boat. How do I know? I have fished many V hull boats including my Blackfin. When slow trolling they roll. When on plane they have a ride like no other.

Wzdr02 said:

My thinking is to buy a 36 to 44 foot liveaboard V hull if I can't find a trawler I want. We intend do do this every winter from Florida to the islands. What is the draw back other than a little fuel economy more wear on the engines BUT you can go fast if you need to.

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If your intent is to purchase a boat designed for planing, be aware that the power plant(s) will most likely give you enough power to get up on plane. That's what the manufacturer designed the boat for, afterall.

If it has Diesel engines, running them at far less than their load ratings will in fact damage the engine, especially with older naturally aspirated ones. When I repowered my boat, conventional thinking would have me place a Diesel engine with similar torque as the gasoline engine I previously had. However, my intent was to run my boat only 6 knots. I needed to make sure the engine was adequately put under load at that speed. That's why I went from a 260 horsepower GM 350 block to a 48 horsepower Perkins 4.108. If the engine isn't properly loaded, it will not only run inefficiently, it will not be able to get up to operating temperature and hence will experience excessive wear on all parts. It will also not be able to get proper lubricity if it is not running at proper operating temperatures.

This is something to give a considerable amount of consideration to. If your cruising speeds are not going to place a load on a Diesel engine that falls in the range it is rated for, you will considerably lessen its life.

Gasoline engines are a different monster. They are easy and cheap to rebuild and replace. If you underload it and it gives you a few hundred less hours, you've saved enough in fuel costs to justify it. But then again, an average marine gasoline engine will likely last 2000 hours if properly maintained.

An average naturally aspirated marine Diesel engine will last 8000 hours if properly maintained. So take your pick, but also understand the stakes involved in underloading a Diesel engine.

convert CC 47 Commander to Trawler

Hello: I'm Sam and new here. Thinking of converting a 47 CC Commander (there are many out there on the cheap) to cruise at hull speed with occasional offshore (pick weather).

This is a 35,000 boat with a solid hull and motoryacht room. Will need a keel for directional stability and prop protection. Drop in a couple of Lehman or Perkins 120 to 160HP.

The keel should give some roll damping.

Any thought here?

Sam

Hey Sam, you must be crazy.

Sam

kingfish said:

Hello: I'm Sam and new here. Thinking of converting a 47 CC Commander (there are many out there on the cheap) to cruise at hull speed with occasional offshore (pick weather).

This is a 35,000 boat with a solid hull and motoryacht room. Will need a keel for directional stability and prop protection. Drop in a couple of Lehman or Perkins 120 to 160HP.

The keel should give some roll damping.

Any thought here?

Sam

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I would drop in a couple 80hp rebuilt anythings...cheaper the better. 120 and on up..if they can't plane the boat...just wasted cubic inches of hp.

I thought I would do the same if I didn't find a trawler to my liking at the right price.

If you can do all the work yourself and consider the result one step above a throwaway boat the go for it....otherwise not many will buy into it 10-15 years down the road possibly (the right person will buy it...just finding them is the trick).

It's probably not worth it if you have to pay for the conversion over the $10-15 grand the engines will cost.

Sam's not crazy at all.

But it would be much better if the stern was rebuilt to a full displacement shape. Curved up aft w the transom out or nearly out of the water.

You'll burn 1/3 less fuel and require that much less power. But it will never plane again.

And to be cost effective you'll need to do most of the work yourself.

I seriously doubt that unless a person cruises tens of thousands of miles a year that altering the hull would ever pay off.

They would have to be very comfortable in design and construction of hull extensions or they could actually make things worse and/or just piss away the money and time and have to pay for it to be done by others...yes it can be done...but I know so few that would even attempt that as compared to a repower to smaller less powerful engines.

That's true Scott but people do bigger jobs for less benefit.

And w careful cutting one could bend the existing bottom planks upward to form a graceful curve. Downside is the planks would need to be slightly longer but one could also shorten the boat a tad and move the transom fwd. Or the transom fwd just at the bottom.

With FG a sawsall may be your friend. And bending is still possible. Much planning would make things go smoother and result in a better job.

Also installing a flat surface like a big pice of plywood under the stern angled up to the bottom of the transom and water line may be a bit funny looking out of the water but almost just as effective.

Cost effectiveness would depend on resale value too and that could be positive or negative. But w so many people running big fast boats slow it should be a plus at time of sale. Unless the mod job was a terrible hack job.

The new stern would be better in following seas and more maneuverable in the harbor too. I assume bigger rudders.

I guess two big questions are... glass or wood? Seaworthy or ICW worthy?

manyboats said:

Sam's not crazy at all.

But it would be much better if the stern was rebuilt to a full displacement shape. Curved up aft w the transom out or nearly out of the water.

You'll burn 1/3 less fuel and require that much less power. But it will never plane again.

And to be cost effective you'll need to do most of the work yourself.

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Hull alteration sounds good, technically, but it also strikes me as diminishing returns. Inexpensive boat, inexpensive repower (OK, relatively... and Sam, remember the genset, too, if you're starting with gas)...

But saving -- maybe up to, maybe not -- 1/3 of fuel costs when it's already been dropped to relatively low numbers...

Means a lot of work for a little gain. Could be actually using the boat sooner by skipping that step...

-Chris

V Hull

Well your all understanding where I'm heading. No repower but there are many boats with V Hulls and good engines. Any mid 80s boat I buy will be a throw away when we are done 10-15 years from now. I like the idea of speeding up every now and then.

V Hull Viking or Hattaras

So.... To liveaboard florida and the bahamas and the islands, a Viking or Hattaras in the 40-44 foot range is a bad Idea?

Firts of all any boat cruising at hull speed is very very expensive.
Hull Speed is a sailors concept , enough free wind and even a Tahiti Ketch can do it.

Cruising at SL, (the square root of the waterline) is the usual cheap spot,actually .9 to 1,15 times SL, depending on the boat.Light skiney boats do better than fat heavy roomarans.

Cruising at hull speed, SL times 1.34 will cost at least 2x the fuel, and on many boats 3x the SL fuel burn.

On some lighter boats it is actually cheaper to get up on the plane , where wave making resistance drops , and the nautical MPG goes down.

Puttering about at trawler crawler speeds is fine in an old high speed vessel, just forgetabout hull speed, you cant afford it.

Yes on some engines there will be under loading damage , the engine will begin to slobber , but it takes a long time.

IF we accept say 8000 hours as a service life , and the engine has 2000-3000 when you purchase the boat , 5000-6000 should be left.

So if the engine life is cut in half , SO WHAT?? most folks do not put on 3000 hours in a lifetime .

A better prop for low speed , and oil analysis with more frequent changes will help.

The round trip would be totally destroyed by getting a $30K boat and creating a bastard for another $20 $50K , then attempting to find someone in love with the concept, with $50 to $80K burning a hole in their pocket for a $30K boat.

Droping in a pair of engines sounds easy , it is if you have done a few ,and have all the equipment,, but if a yard will do the work, !!! check with folks who have done it for pricing.Carry smelling salts.

Very well said Fred,

If you're into really radical ideas take out half the pistons, pushrods ect ect and reduce the displacement by 1/2. Would probably be a little less that 1/2 of the original power due to the drag or friction of the bigger engine parts. And all it would be is labor.

Has this ever been done?

Wzdr02 said:

So.... To liveaboard florida and the bahamas and the islands, a Viking or Hattaras in the 40-44 foot range is a bad Idea?

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Don't think I saw where anyone said that. I'd probably even go bigger, budget permitting, since living aboard can get a bit cramped... for me. Couldn't do it on our 42 sportfish. Might be better (more room) on a motor yacht in that range, if you like that sorta thing. YMMV.

-Chris

FF said:

Firts of all any boat cruising at hull speed is very very expensive. Hull Speed is a sailors concept , enough free wind and even a Tahiti Ketch can do it.

Cruising at SL, (the square root of the waterline) is the usual cheap spot,actually .9 to 1,15 times SL, depending on the boat.Light skiney boats do better than fat heavy roomarans.

Cruising at hull speed, SL times 1.34 will cost at least 2x the fuel, and on many boats 3x the SL fuel burn.

On some lighter boats it is actually cheaper to get up on the plane , where wave making resistance drops , and the nautical MPG goes down.

Puttering about at trawler crawler speeds is fine in an old high speed vessel, just forgetabout hull speed, you cant afford it.

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I think I understand your point, but I'd say words like "very, very" can cover a very, very wide range.

Our hull speed (LWL of about 39') is approx. 8.4 kts, and our nominal fuel burn at ~8.2 kts gives us about 1.7 NMPG. SL is about 6.3 kts, and we get about 2.9 NMPG at ~6.5 kts.

Yes, 1.7 is very, very bad compared to 2.9. And yes, cruising at SL is relatively cheap (in the grand scheme of "things boat" compared to theoretical hull speed.

OTOH, when we cruise at ~22-23 kts, where the hull is usually most comfortable when were on plane, we're only getting about .7 NMPG.

So there's very, very... and then there's very, very.

-Chris