Riva Superamerica 48

Could you help me evaluate the performance and safety of the Riva Superamerica 48 in heavy seas, say typical east Mediterranean short waves, strong winds... say gale force winds? Here is my experience with the boat so far and some of the questions I have been pondering:

- Old but solid design, mine was built in 1980
- 48 ft overall, 41 ft LWL, current displacement 14 tons, 12 degree deadrise angle
- In my opinion, minimal superstructure compared to other examples, see photos
- Powered by 6CTA 450 Cummins, max speed 31 knots (approx. 1.2 tons lighter than originals)
- Original engines were VT903s, leaflet max speed was 26 knots
- Has one real fully watertight bulkhead behind the crew cabin in front
- Two bulkheads (in front and behind engine compartment) can be made watertight with minimal effort (I have not seen many designs in this size that can have three real watertight bulkheads)

The boat has been in medium weather in the Aegean sea (force 6-7) on long passages. When running into the waves, I need to reduce speed to prevent pounding but otherwise no issues. Sometimes, a bigger wave could swamp the whole boat (bow is pretty low) but I never felt uncomfortable. Still, it was hard to make more than 11-13 knots to prevent jumping from one wave to the next. When running in beam seas (force 4-5), the boat would roll a lot at times but snaps back fairly quickly. A higher speed could be maintained 14-15 knots.

Some of my questions. Would another boat design of similar displacement give me significantly higher speeds or higher margin of safety? What are the dangers when seas build up? If a wave rolls the boat, will it come back immediately? It looks from the design that it has fairly good stability. How quickly would the engine compartment flood through the side air intakes? It looks as if even inverted, the intakes will be above the water? Is this really a concern? Are there ways to close them automatically or may be find alternative source of air in heavy weather? Would it make sense to install tanks in the bilge areas along the keel and in the lazarette, all below the waterline, that could be used either for fuel or as water ballast to improve stability and trim? Especially, since I have 1.2 tons of displacement headroom due to the lighter engines. Is this ever done? Why or why not?

Thank you.

 

Welcome to the forum.
Beautiful boat, congrats.
To answer some of your questions, with concrete data, not with simple opinions, it would be necessary to study the plans of the boat and carry out quite a few calculations. Do you have the plans?

 

Thank you. I do not have the plans but I will take opinions

 

If you are not already a member of the YBW Forum in England, then please do sign up and copy your post above to their Motor Boat Forum -
Motor Boat Forum https://forums.ybw.com/forums/motor-boat-forum.14/

I can (almost certainly) guarantee you that you will receive an enthusiastic response on this Forum - there are quite a few posters on there who have similar sized motor boats in the Mediterranean.
Including one gentleman who has an Itama - he will find your question below quite irresistible, and he will probably tell you that an Itama is far superior.

 

Going back to this thread, I found some plans of a similar boat, this is the link (in Italian).
G.S.C. Riva - Technical drawing of the 50 Superamerica Special HP model - Google Arts & Culture https://artsandculture.google.com/asset/g-s-c-riva-technical-drawing-of-the-50-superamerica-special-hp-model/JwGHJFaJvv1KVw?hl=en

The technical drawing above is for the 50' model, where the hull has been lengthened by 2.5 ft, 1 ft in the area of th tanks and 1 ft in the cockpit area and the engines are a little bit bigger. MAN 510 hp, vs. the original VT903Ms (and further my current engines are Cummins 450C (430 hp). The other difference I see is that in the diagram above the 50' transom angle is 16 degrees while when I measure mine, I get 12 degrees but not sure if I am measuring accurately.

So, my questions now are, can I use the diagrams above to produce a model of the hull that I can play with it? Specifically, I would like to know the downflooding angle (if I should do something about the air intakes, i.e. automatic closure in rough weather and alternative air source) and then how much can I load up this boat with fuel with acceptable stability (i.e. can I put an additional 10,000 lb of fuel bladders?). What would be a good software to use where I can start with a similar hull then modify it based on this drawing?

Thank you.

 

I really don't think you can do anything reliable with that plan. Not only is the length different, but the beam of the hull will probably be different as well. In any case, deducing the hull shapes with that information is impossible. On the other hand, to make the calculations you want to do, you would need to know the ship's light weight and its centre of gravity.
Once you have all that, you will need to carry out a series of calculations for which, in addition to good software, you will need to have a clear understanding of various concepts of naval architecture.
A very good software is Maxsurf. It is quite expensive but with the trial version, which I think allows for 15 or 30 days of use, you will be able to study everything you need.
Good luck and keep us informed of your progress.

 

@Ithaka , if you think I can help you with anything, just say so.

 

A vessel of this size should not be out in gale force winds, that is a big sea for such a small boat.
You should plan your route in advance to avoid such weather.

It is not the head seas, that is the issue, it is the following and stern quartering seas that become the issue, especially when offshore.
These are the ones to avoid, since your vessel has much more buoyancy aft, and as such, shall be 'picked up' by a stern wave and burying the nose forward (less buoyancy), most likely into the wave ahead or worse, into the trough - a classic broaching situation.

I would advise against "planning" on running in those type of sea states.

You may find the attached of some use too.

 

Ad Hoc is a respectable naval architect; his words deserve careful heeding and you are fortunate he spoke. I could end here.

As a casual lover of boats; your vessel only shows a beam of 13.7 feet, unless the data I found is wrong. This beam (if accurate) and the bow shape along with the trim changes greatly reduce her safety margin. Some of these are inherent; unchangeable.

Vessel beam is a direct correlation to the vessel’s transverse stability and no magic increases it. Your query as to what happens deserves an answer, I’ll not give it, but if you dive into a trough head first or get rolled sideways; it would not be certain the vessel would recover. Damage is also not something I can guess.

Flooding the bilge or loading it more is a rather terrifying extreme boaters incorporate for vessels that are too lively in big seas; I see no reason it ought to be considered. However, if the vessel is indeed above her lines aft after engine mods; it might be wise to consult with an NA about getting the trim back as the bow is indeed low as designed and thus lower with a high stern. Whether tankage or lead is another discussion.

Taking some measurements against known waterline might offer you some ideas about the effect of your mods. But if the stern came up; the bow went down some.

I’m a little surprised you are seeking methods to push the envelope. I’d avoid fast seas over 3M if the boat were captained by me.

I’d like to hear from wiser men an answer to your query about a different vessel in similar category. I’d start off by suggesting finding a wider beam boat in the simplest sense. Consider looking at boats in terms of length to beam. A 36 foot boat with a beam of 12’ has a ratio of 3. A 48 foot boat with a ratio of 3 would have a beam of 16’. The 48’ boat would be comparable ito stability. The reason the Riva is not 16’ wide is she’d be far more inefficient, etc.

Anyhow, mine is a casual, friendly comment. The boat is beautiful, by the way.

 

Thank you all for the comments, warmly appreciated. For sure, I do not seek to run the boat in big seas but sometimes it happens and part of this discussion is focused on making myself and the boat more prepared when and if it happens. It is also a little of an intellectual challenge exercise vs. a real situation to be fair.

I can attest to what Ad Hoc is suggesting, when running with the sea in bigger waves, the boat broaches. Then, while I try to recover and point with the waves, she heels, sometimes a lot. My biggest concern is that when it heels it could start taking water through the engine air intakes. So, the purpose of this exercise is to see what I can do to improve the sea worthiness of the boat given the design constraints. One idea was to install some covers for the engine air intakes that I can remotely close and open. What would be examples of such devices? Then I want to improve the water tightness of the various sections, for example the bulkhead between the bow and the master cabin is solid with no openings but the bulkhead between the engine compartment and the lazarette has numerous gaps around the engines exhausts that need to be made watertight.

Another question, it is often said that a deeper-V helps in head seas because it reduces slamming but isn't it also a hindrance in following seas because the boat is less maneuverable when the wave overtakes the boat?

Then comes the issue raised above, that following the engine upgrade and replacement of various heavier systems (fridge compressors, air conditioners, etc. with modern lighter devices), the boat is approx. 1 ton lighter at the stern. This is good for everyday use (better fuel efficiency, max speed increased from 26 to 31 knots) but not optimal in a broaching situation. My proposed solution to that would be to install additional tankage in the lazarette and the bilge between the engines and have the option to transfer fuel (or, in a dire situation, flood them with seawater) to balance the boat. I read somewhere that the destroyers in WWII in the Pacific would flood their fuel tanks with seawater in big seas. I understand it has to be in a few secured/sectioned tanks (to avoid free surfaces) but I am not sure exactly where to position the tanks. One idea I had was to use 3-4 inflatable mattresses (very cheap, they hold around 300 liters of water each) to experiment with different locations, then once I figure out a good setup to order proper tanks. I thought that if I could model this in some software, it would be easier than playing around with the mattresses in a controlled environment. I do not want to add lead or fixed weight because 98% of the time I actually enjoy the lighter weight and the improved efficiency.

The last question is, would the boat recover if she rolled over, assuming I make the bulkheads and the bridge to cabin openings watertight and nothing (windows) breaks. I would even consider a static test in the marina (with a crane) but I do not want to go to 90 degrees. So again, if you guys can point me to some calculations, i.e. do a static test to 50 or 60 degrees, then use a formula and that would be representative, that would be helpful.

Thank you again.
MV Ithaka

 

To carry out the calculations and numerical simulation of the studies you propose, it would be necessary to have the body lines plan or a table of offsets or a reliable 3D model.
By the way, ballast/fuel tanks are totally prohibited.

 

Simple, exercise good seamanship...do not go out in sea states that your boat is not designed for...and check the weather reports before departing.

You're again, missing the point.
Read the MGN 328 notice.

Now you are in fantasy land.
Your line of questioning verges on negligence and arrogance.

If you continue down this train of thought...sadly, we shall be reading about the loss of your vessel, and possibly life, in some future news bulletin.

 

if he is above his lines aft; he could pour an epoxy/lead ballast, could he not?

I don’t understand your comment. If he lightens the ship; he certainly has recourse to correct it.

Unless you mean ballasting with fuel is not permitted?

 

@Ithaka

Ad Hoc is being kind offering a reply you may not enjoy. He doesn’t usually engage nonsense at all.

If you want to travel in those seastates; the vessel is not the right one. It is that damned simple.

As for your trim issues; you hire a NA.

 

I found a good article for you to read. Or at least one I think may help you course correct. These are planing designs that are capable of bigger seas.

Ray Hunt Design | Pilot Boats | The Hunt Deep-V Pilot Boat Explained http://www.rayhuntdesign.com/commercial-pilot-deepv-pilot-boat-explained.php

Also, it may be a fun exercise for you to contact Grand Banks and ask them about the safe seastate for their vessel the Eastbay 44. It looks a bit more capable than yours with a better bow and wider beam, but not by much and it may help you establish a baseline if they offer you any advice. At a range of less than 500nm; the Eastbay is not a bluewater design, nor is yours.

Eastbay 44 https://www.grandbanks.com/models/eb44