What make is my boat

[Cadence]

I think she might be a little under powered, if not tournament fishing who cares. If you opt to go with twins make sure to consider the weight. The 4 cycles are heavy and hung well aft. Maybe check the weight per HP. A couple of 15s might give you redundancy without making her stern heavy.

[MicHughV]

Your typical center console fishing boat is capable of running at full bore thru' some big seas, this means a pretty stout hull design. The engines weigh close to 500 lb apiece, a full fuel tank is close to 1,000 lbs, etc, the boat is double skinned, etc, etc, and has a fairly robust longitudinal stringer support system.

I think your boat is likely more than 1 ton ( 2,000 lbs), just doing some simple math (in feet), length x beam x draft x weight of water x hull shape factor will give an approximation of the displacement...at a rough guess, I come up with at least 4,000 lbs....it might be more.

[Mrmaw]

I'm looking forward to taking her out on her maiden voyage in the new year so I can see how the engine performs, she's fitted with a garmin striker 7sv so it will give me the speed and I can decide from there wether or not to go with the twin engine idea. She's a work in progress at the moment and over time I'll get her suited to my needs . As long as I can take my son out for a relaxing spot of fishing I'm happy. I appreciate everyone's input and suggestions. Have a great Christmas and a happy new year. I'll upload a photo of our first catch . All the best, Mark.

[jimbunyard]

Originally Posted by Mrmaw

Wow, twin 150hp engines. Have you recently had a lottery win ? Good fishing grounds are about an hour away from my mooring so I'm hoping a full tank will last me there and back. At some point in the future when finances allow I would like to double up the 25hp and I would hope that would get her up on the plane but until I get chance to try the single outboard I'm not sure.

An hour away at what speed?

While the hull is definitely designed as a planing one, with a 25, or even two, she'll never get on one, especially with all that superstructure.

Hull speed for a 19 foot length water line (LWL), displacement hull is about 7 MPH; since this isn't really a displacement hull, and it has fairly shallow deadrise, you might get a little more out of her with the 25, but probably not more than about 10. The high thrust O/B will help some.

The good thing is that you should get pretty good mileage; unless the boat is seriously overbuilt, I'd be very surprised if she weighs even a ton; with the 25 hp, I'd guess about 1500, especially given the way she's floating in the picture in your 2nd post...

An estimate to turn her (back?) into a planing boat would be at least 100 hp, probably 125 or even 150 with all the wind resistance added by the cabin.

I also note that the transom appears to be curved. Is that an optical illusion , or is it actually curved? If so, is that the way it was designed, or has the transom been overloaded?

You said earlier that it may have been used in some sort of law enforcement role. Have you thought about enquiring about it's past amongst some of that crowd?

[TrentePieds]

JimBunyard said: "An hour away at what speed?"

Not much of a concern. Nowhere in the Solent, can you ever be more than about 2 NM from shore. From the City of Southampton down Southampton Water to the Solent is about 8NM, and Southampton Water itself is about a mile wide at its widest.

I wouldn't like having to use this little boat off the coast of, say, Louisiana, but then neither I nor the OP will have to do that :-)!

I would think that in the Solent, she'd be just the cat's pajamas for a spot of fishing, as indeed she would be in Danish inland waters and around the corner up along the Swedish east coast.

TrentePieds

[Mrmaw]

I've tried to upload a video but it won't upload of a boat that's very similar dimensions to mine running a single 60hp mariner. At a guess I'd say she's doing 20 knotts so surely twin 25hp outboards would get mine on the plane ??

[Mrmaw]

My previous boat had a 16hp lister cruising at around 6 knotts, that boat would take an hour to get to the fishing grounds. I'm hoping my new vessel will achieve at least 12 knotts with her 25hp so should cut the journey by half

[jimbunyard]

Originally Posted by TrentePieds

JimBunyard said: "An hour away at what speed?"

Not much of a concern. Nowhere in the Solent, can you ever be more than about 2 NM from shore. From the City of Southampton down Southampton Water to the Solent is about 8NM, and Southampton Water itself is about a mile wide at its widest.

I wouldn't like having to use this little boat off the coast of, say, Louisiana, but then neither I nor the OP will have to do that :-)!

I would think that in the Solent, she'd be just the cat's pajamas for a spot of fishing, as indeed she would be in Danish inland waters and around the corner up along the Swedish east coast.

TrentePieds

Well I think the boat is perfect for some local fishing too, and you might be surprised at what that particular one could do around here (as compared to a 16 ft flat with a 18 horse everrude), but if the desired fishing ground is an hour away at 20, then it's 2 hours away at 10...

Originally Posted by Mrmaw

I've tried to upload a video but it won't upload of a boat that's very similar dimensions to mine running a single 60hp mariner. At a guess I'd say she's doing 20 knotts so surely twin 25hp outboards would get mine on the plane ??

One has to have 'special powers' to upload videos here; most link to an already uploaded one, though I can just copy and paste the url of utube videos and it'll automatically load the thumb. It's all above my paygrade...

As for the speed you get, I'm just going by what I see in a couple pictures, and extrapolating from there. If the boat is very light, as it appears to be in the pictures where it's shown floating, with the wide flat stern she may do alot better, early planing-wise (especially if that relative flatness is carried very far forward) than boats with more severe deadrise.

The high torque prop on the 25 you have now may give you a benchmark to go by, and maybe you can get a cheap 'normal' prop to use as a comparison; if either gets you close, maybe a 60'll do it. (But she's gonna be very sensitive to weight, so maybe catch and mostly release might be in order...)

For instance the wide, flat, light aluminum fishing boats commonly used around here basically 'plane' whilst they're sitting still; a 25 hp on a 16' flat will usually get you close to 30, long as they're not loaded to the gills...

[MicHughV]

One last thing to consider...most planing hulls have what are known as "lifting strakes", in essence narrow ski like surfaces running the lenght of the hull, that are parallel to the water. they are not wide, maybe a few inches and typically, there will be 3 or so each side of the center line. The center line is usually also flat, a few inches wide.

I'm speaking in generalities here, as every planing hull maker touts their particular design as being better than the competition.

Nonetheless, these "lifting strakes" provides that flat ski-like surface to enable the boat to rise up out of the water, thereby reducing the friction between boat and water, enabling the boat to come on plane.

This is a kinda long winded explanation, but I do not see any indication that your boat has these " lifting strakes". That is not to say, your boat couldn't plane, given sufficient power, but I'm doubtful that a second 25 hp engine will do the trick.

You can't assume you'll be running in flat calm water either and your estimated 12 knot boat speed is optimistic.

My guess is that you will likely move at around 6 knots with your current setup, and not much better with twin 25's, though each engine will likely run at a lower rpm.

That prop is a dead give away that you are likely pushing a displacement boat.

Your existing 25 liter fuel tank is insufficient in my opinion, if you plan to run 6 miles out to sea, you will likely use half your fuel, and you have left yourself no " reserve" to get back.

Common sense should tell you, to give you and your boat some trial runs in protected water to give you a first hand idea of exactly what your boat is capable of doing and likely fuel burn.

Let us know how it goes.

[jimbunyard]

Forgot to add, two 25s are going to be marginal, and what might make the difference is the drag induced by having two lower units in the water.

In other words, a single 50 or 60 might get you on plane whereas 2 25s or 30s might not...

That is, if it's actually a planing hull.

[MicHughV]

People don't think about this, but the immersed leg of an outboard provides a lot of drag, especially so at speed.

I often fish for kingfish, which requires a boat to be crawling along, as you will be pulling live bait.

On my boat, I will kill one engine, and go along with just a single engine at idle speed, but even that is too fast. In the past, I would raise the non running engine, but have learned to keep the non running engine in the water to induce sufficient drag to slow me down.

Interestingly, there is a video on Youtube that shows two identical boats, one fitted with twin 150's and one fitted with a single 300 hp Yamaha on a test lake. Both boats are run back and forth, side by side to compare acceleration, top speed, fuel burn, etc,
and the results are tabulated at the end.

There are other video's available that delve into the drag a lower unit causes at different speeds. It is quite significant. Adding another engine obviously provides more power, but also more drag, which must be overcome.

It's a fascinating science. I can also recommend reading "The Propellor Handbook" authored by Dave Gerr. The book is a complicated and lengthy read, but Dave covers just about anything you might want to know about engines, boats, propellors, etc, etc.
The book also offers various ways by which you can tabulate potential results of your own particular boat.

About a half dozen pages of calculations is to be expected to arrive at an answer

[MicHughV]

this is the link to the outboard comparo

https://www.youtube.com/watch?v=gG_-YmGN8SY

[Adelie]

Originally Posted by Mrmaw

My previous boat had a 16hp lister cruising at around 6 knotts, that boat would take an hour to get to the fishing grounds. I'm hoping my new vessel will achieve at least 12 knotts with her 25hp so should cut the journey by half

Planing speed is about 2xHull speed. In between is plowing speed which involves serious amounts of power to slightly increase boat speed.

Once on a plane you can back off the throttle. Doubling power will not get you on a plane, 4x or 5x might.

Sorry to pop you hopes.

[Mrmaw]

This is the Shape of the hull

[ranger58sb]

Originally Posted by Mrmaw

I'm surprised to hear she weighs so much being only 23ft . I would hazard a guess that my boat would be around 1 ton so I'm thinking twin 25hp or a single 60hp would be man enough

Think I'd prefer a single 60 to smaller twins. Or if that's just not quite enough, maybe a single 75 if there is such a thing. Or at least a single of whatever max horsepower you can safely and sensibly hang on there. (As long as the transom can stand the weight and torque.)

Wouldn't surprise me if maintenance on smaller twins might be almost double what it would be for a larger single.

Plus 2x leg drag.

I'd guess it's cheap enough to buy unlimited towing insurance in your neck of the woods.... but then a new or almost-new well-cared-for modern outboard can generally be pretty reliable.

-Chris