Semi displacement conversion to outboards

[fallguy]

Generally less fuel than a "planing" type hull of similar size and displacement. Low resistance as long as they are not loaded so that the stern is deeply submerged. The lobster boats have very little deadrise at the transom and moderate deadrise amidships so tend to low resistance unless heavily loaded. Very little if any "hump" when accelerating. Not the boat to use for jumping waves though. Outboard versions typically have a shallower and smaller skeg/keel than needed on inboard versions to accommodate the shaft and propeller.

So, they are gonna pound you to death with the low dr at the transom?

 

[DCockey]

"Planing rails" would be unproductive, I'd say.

If "planing rails" are strips which run along the turn of the bilge then they are common on Maine lobster boat type hulls. The builders and owners of the boats are convinced they are worthwhile.

The Sisu 22 is a popular design which has been around for over 40 years. Originally inboard powered they now have an outboard on a bracket. The design was modified in the 1980's or so with built in spray rails which improve high speed behavior. Eastern currently builds the Sisu 22 though I believe there are other molds around. https://www.easternboats.com/22-sisu

https://www.soundingsonline.com/boats/sisu-22

 

[Mr Efficiency]

So, they are gonna pound you to death with the low dr at the transom?

Not really, they are not going fast enough to take ballistic trajectories off large swells, and have sufficient boat length to handle shorter chop without exposing the flattish aft bottom.

 

[DCockey]

So, they are gonna pound you to death with the low dr at the transom?

If you run fast enough into large enough waves they will pound. Solution is to throttle back. That's the tradeoff for the low resistance and minimal hump. No single design does everything well.

 

[Mr Efficiency]

If "planing rails" are strips which run along the turn of the bilge then they are common on Maine lobster boat type hulls. The builders and owners of the boats are convinced they are worthwhile.

The Sisu 22 is a popular design which has been around for over 40 years. Originally inboard powered they now have an outboard on a bracket. The design was modified in the 1980's or so with built in spray rails which improve high speed behavior. Eastern currently builds the Sisu 22 though I believe there are other molds around. https://www.easternboats.com/22-sisu

https://www.soundingsonline.com/boats/sisu-22

If they were not original to it, you would wonder why. I sense he is looking for more speed, and thinks these rails might go toward delivering it. At its current cruise speed, I'd doubt they'd be beneficial, you don't get much lift frim such things at modest speeds, unless the boat is light. Top speed might be up a little, but top speed should not dictate much.

 

[DCockey]

Owner's report of speed and fuel consumption of a Hunter Alura 30 with a Diesel inboard: 30' Luhrs Alura Owners?? Just Purchased MY 1987 30' Luhrs Alura & Loving It! Page: 1 - iboats Boating Forums | 10617865 https://forums.iboats.com/forum/general-boating-outdoors-activities/boat-topics-and-questions-not-engine-topics/10617865-30-luhrs-alura-owners-just-purchased-my-1987-30-luhrs-alura-loving-it

The Hunter Alura 30 has built in "spray rails"/chines based on photos in these websites and the video. It is also interesting that the boat in the first website has a smaller skeg/keel than the boat in the photos above:
1987 30' Luhrs Hunter Alura for Sale - The Hull Truth - Boating and Fishing Forum https://www.thehulltruth.com/boats-sale-wanted/814286-1987-30-luhrs-hunter-alura-sale.html

Boat for sale - Hunter Alura 30 Offers encouraged - 30' http://www.boatersresources.com/bfs_detail.php?adid=411412
1988 Alura 30 Classic New York - Oakdale Yacht https://www.oakdaleyacht.com/boats-for-sale/1988-alura-30-classic-new-york-5882215/

wildsideboats - Do you currently own the hull or is this a project you are considering?

 

[Mr Efficiency]

Knocking down spray helps gain a little speed, but he speaks of "full length planing rails". At 20 mph not going to do much, and pretty redundant toward the flat stern.

 

[DCockey]

I wonder if he has actually seen the boat. As I said in my note above the design already has full length integral spray rails / chines.

 

[Mr Efficiency]

I wonder if he has actually seen the boat. As I said in my note above the design already has full length integral spray rails / chines.

I noticed the bow area, couldn't see what else was there further back, I would not be going down the track of putting any more on it. I think if not happy to cruise at 20 mph, go to a planing hull. you can't really stretch these types of boats into speed machines, not sensibly anyway. And the outboard conversion option needs an existing, successful example as a template, or too risky. Why be the guinea-pig !

 

[wildsideboats]

All good input and much appreciated . Yes this post is to see if anybody has attempted this or similar conversion . I am a fiberglass boat builder / restorer . I do ovvn this boat and plan to use it for fishing / diving / cruising . High speed is not my greatest concern hovvever I vvouold like to cruise at 18 to 20 kts. I have installed these lift/spray strakes on tvvo similar hulls and it made a remarkable improvement on both. Im in the process of removing the balsa core from the hull, Ive reached the engine room forvvard bulkhead and had a " I vvonder " moment.... I vvonder if anybody has ever put outboards on one of these ? Because Im at the stage of either rebuilding the engine compartment for an IB or use that space for something more creative . Just a shot in the dark, makes for interesting conversation if nothing else...

 

[fallguy]

Isn't locating the strake difficult, when the waterline is changing? Ot do you jist build it long and down below the WL aft to above the WL forward and guess some?

 

[DCockey]

Based on the photo of the corner of the transom the inverted extending from turn of the bilge is very similar to the Sisu 22.

Is the black rubber extrusion what you are planning to use as the lift/spray strake? Will you follow the existing chine with it?

What is the "Anne Elise"?

 

[wildsideboats]

Yes, basically doubling the vvidth of the lifting strake. Photo of boat is just a boat that looks similar to vvhat this boat vvouold look like vvith OBs.